Typo in Prerequisites and incorrect variable reference in extraction call

[schwentker]

1. Prerequisites typo (same as previous exercises):
   In the Prerequisites section:

Current:
Prequisites

Should be:
Prerequisites

This is the same spelling error found in exercises 2, 3, 5, 6.

2. Variable reference error:
   In the create_ai_extract call, there's an incorrect variable reference - I think:

Current:

ai_response = client.ai.create_ai_extract(
    prompt,
    [AiItemBase(id=file.id)],  # 'file' is undefined here
)
Should be:
pythonai_response = client.ai.create_ai_extract(
    prompt,
    [AiItemBase(id=file_id)],  # Should use 'file_id' variable
)
The code uses file.id but file is not defined in that scope - it should use the file_id variable that was set in the previous code block.