diff --git a/lib/problems.rb b/lib/problems.rb
index 61bcaa5a..26d6fbfa 100644
--- a/lib/problems.rb
+++ b/lib/problems.rb
@@ -1,9 +1,54 @@
-require_relative './stack.rb'
+require_relative "./stack.rb"
 
 def balanced(string)
-  raise NotImplementedError, "Not implemented yet"
+  return true if string == ""
+
+  parens_hash = {
+    "(" => ")",
+    "[" => "]",
+    "{" => "}",
+  }
+
+  stack_parens = Stack.new
+  string.each_char do |paren|
+    if parens_hash[paren]
+      stack_parens.push(parens_hash[paren])
+    else
+      return false if paren != stack_parens.pop
+    end
+  end
+
+  return stack_parens.empty?
 end
 
 def evaluate_postfix(postfix_expression)
-  raise NotImplementedError, "Not implemented yet"
-end
\ No newline at end of file
+  operand_hash = {
+    "+" => true,
+    "-" => true,
+    "*" => true,
+    "/" => true,
+  }
+
+  stack_postfix = Stack.new
+  postfix_expression.each_char do |char|
+    if !operand_hash[char]
+      stack_postfix.push(char)
+    else
+      digit2 = stack_postfix.pop.to_i
+      digit1 = stack_postfix.pop.to_i
+
+      case char
+      when "+"
+        value = digit1 + digit2
+      when "-"
+        value = digit1 - digit2
+      when "*"
+        value = digit1 * digit2
+      when "/"
+        value = digit1 / digit2
+      end
+      stack_postfix.push(value)
+    end
+  end
+  return stack_postfix.pop
+end
diff --git a/lib/queue.rb b/lib/queue.rb
index 828217c6..94490ee5 100644
--- a/lib/queue.rb
+++ b/lib/queue.rb
@@ -1,31 +1,63 @@
 class Queue
+  QUEUE_SIZE = 20
 
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = Array.new(QUEUE_SIZE)
+    @front = @rear = -1 #-1 because it is not index in array, bc front and rear float around we dont know there will be any particular value
+    #use -1 to indicate the queue is empty
   end
 
   def enqueue(element)
-    raise NotImplementedError, "Not yet implemented"
+    if @front == -1 # queue is empty
+      @front = 0
+      @rear = 0
+      @store[@rear] = element
+    elsif @front == (@rear + 1) % @store.length # queue is full
+      raise Error, "Q full"
+    else # queue not empty
+      @rear += 1
+      @store[@rear] = element
+    end
   end
 
   def dequeue
-    raise NotImplementedError, "Not yet implemented"
+    if @front == -1
+      raise Error, "Q is empty"
+    elsif @front == @rear
+      removed_value = @store[@front]
+      @store[@front] = nil
+      @front = @rear = -1
+      return removed_value
+    else
+      new_front = (@front + 1) % @store.length
+      removed_value1 = @store[@front]
+      @store[@front] = nil
+      @front = new_front
+      return removed_value1
+    end
   end
 
   def front
-    raise NotImplementedError, "Not yet implemented"
+    if @front == -1
+      raise Error, "Q is empty"
+    else
+      return @store[@front]
+    end
   end
 
   def size
-    raise NotImplementedError, "Not yet implemented"
+    return @store[@front..@rear].length
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    if @front == -1
+      return true
+    else
+      return false
+    end
   end
 
   def to_s
-    return @store.to_s
+    return @store[@front..@rear].to_s
   end
 end
diff --git a/lib/stack.rb b/lib/stack.rb
index cfc6ef0f..8757bdeb 100644
--- a/lib/stack.rb
+++ b/lib/stack.rb
@@ -1,19 +1,22 @@
+require_relative "linked_list.rb"
+
 class Stack
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = LinkedList.new
+    # @top = nil
   end
 
   def push(element)
-    raise NotImplementedError, "Not yet implemented"
+    #If using a linked list for a stack, is there a disadvantage to using a singly linked list and use the add_first method for push and remove_first method for pop?
+    @store.add_last(element)
   end
 
   def pop
-    raise NotImplementedError, "Not yet implemented"
+    @store.remove_last()
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @store.empty?
   end
 
   def to_s
diff --git a/test/problems_test.rb b/test/problems_test.rb
index 9d30e1cd..cea5bad7 100644
--- a/test/problems_test.rb
+++ b/test/problems_test.rb
@@ -1,38 +1,33 @@
-require 'minitest/autorun'
-require 'minitest/reporters'
-require_relative '../lib/problems'
+require "minitest/autorun"
+require "minitest/reporters"
+require_relative "../lib/problems"
 
 Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
 
 describe "Test wave 3 problems" do
   describe "balanced" do
     it "Given balanced strings it should return true" do
-      skip
-      expect(balanced('(({}))')).must_equal true
+      expect(balanced("(({}))")).must_equal true
     end
 
     it "regards an empty string as balanced" do
-      skip
-      expect(balanced('')).must_equal true
+      expect(balanced("")).must_equal true
     end
 
     it "will return false for an unbalanced set of parens" do
-      skip
-      expect(balanced('(()')).must_equal false
-      expect(balanced('(()}')).must_equal false
-      expect(balanced('([]]')).must_equal false
+      expect(balanced("(()")).must_equal false
+      expect(balanced("(()}")).must_equal false
+      expect(balanced("([]]")).must_equal false
     end
 
     it "also works for {} and []" do
-      skip
-      expect(balanced('[]')).must_equal true
-      expect(balanced('{}')).must_equal true
+      expect(balanced("[]")).must_equal true
+      expect(balanced("{}")).must_equal true
     end
   end
 
   describe "postfix" do
     it "can add a 2 numbers together" do
-      skip
       expect(evaluate_postfix("34+")).must_equal 7
       expect(evaluate_postfix("34*")).must_equal 12
       expect(evaluate_postfix("34-")).must_equal -1
@@ -40,7 +35,6 @@
     end
 
     it "can add a evaluate a more complicated expression" do
-      skip
       expect(evaluate_postfix("34+2*")).must_equal 14
       expect(evaluate_postfix("34*2/")).must_equal 6
       expect(evaluate_postfix("34-1+")).must_equal 0
@@ -49,4 +43,4 @@
       expect(evaluate_postfix("62/5+")).must_equal 8
     end
   end
-end
\ No newline at end of file
+end
diff --git a/test/queue_test.rb b/test/queue_test.rb
index 9b616a30..453d959d 100644
--- a/test/queue_test.rb
+++ b/test/queue_test.rb
@@ -1,6 +1,6 @@
-require 'minitest/autorun'
-require 'minitest/reporters'
-require_relative '../lib/queue'
+require "minitest/autorun"
+require "minitest/reporters"
+require_relative "../lib/queue"
 
 Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
 
@@ -11,14 +11,12 @@
   end
 
   it "adds something to an empty Queue" do
-    skip
     q = Queue.new
     q.enqueue(10)
     q.to_s.must_equal "[10]"
   end
 
   it "adds multiple somethings to a Queue" do
-    skip
     q = Queue.new
     q.enqueue(10)
     q.enqueue(20)
@@ -27,13 +25,11 @@
   end
 
   it "starts the size of a Queue at 0" do
-    skip
     q = Queue.new
     q.empty?.must_equal true
   end
 
   it "removes something from the Queue" do
-    skip
     q = Queue.new
     q.enqueue(5)
     removed = q.dequeue
@@ -42,7 +38,6 @@
   end
 
   it "removes the right something (LIFO)" do
-    skip
     q = Queue.new
     q.enqueue(5)
     q.enqueue(3)
@@ -53,7 +48,6 @@
   end
 
   it "properly adjusts the size with enqueueing and dequeueing" do
-    skip
     q = Queue.new
     q.empty?.must_equal true
     q.enqueue(-1)
@@ -65,7 +59,6 @@
   end
 
   it "returns the front element in the Queue" do
-    skip
     q = Queue.new
     q.enqueue(40)
     q.enqueue(22)
@@ -73,4 +66,4 @@
     q.dequeue
     expect(q.dequeue).must_equal 22
   end
-end
\ No newline at end of file
+end
diff --git a/test/stack_test.rb b/test/stack_test.rb
index df5046c8..3511e6a8 100644
--- a/test/stack_test.rb
+++ b/test/stack_test.rb
@@ -1,6 +1,6 @@
-require 'minitest/autorun'
-require 'minitest/reporters'
-require_relative '../lib/stack'
+require "minitest/autorun"
+require "minitest/reporters"
+require_relative "../lib/stack"
 Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
 
 describe "Test Stack Implementation" do
@@ -10,14 +10,12 @@
   end
 
   it "pushes something onto a empty Stack" do
-    skip
     s = Stack.new
     s.push(10)
     s.to_s.must_equal "[10]"
   end
 
   it "pushes multiple somethings onto a Stack" do
-    skip
     s = Stack.new
     s.push(10)
     s.push(20)
@@ -26,13 +24,11 @@
   end
 
   it "starts the stack empty" do
-    skip
     s = Stack.new
     s.empty?.must_equal true
   end
 
   it "removes something from the stack" do
-    skip
     s = Stack.new
     s.push(5)
     removed = s.pop
@@ -41,7 +37,6 @@
   end
 
   it "removes the right something (LIFO)" do
-    skip
     s = Stack.new
     s.push(5)
     s.push(3)
@@ -50,4 +45,4 @@
     removed.must_equal 7
     s.to_s.must_equal "[5, 3]"
   end
-end
\ No newline at end of file
+end