Explanation:

- I looked at my damaged car and wondered how much it would cost to repair it.

- This is the correct choice. "Wondered" is the past tense, aligning with "looked."

- I looked at my damaged car and wonders how much it would cost to repair it.

- "Wonders" is incorrect. It's the present tense and doesn’t fit with "looked."

- I looked at my damaged car and wonder how much it would cost to repair it.

- "Wonder" is present tense. It doesn't match the past tense "looked."

- I looked at my damaged car and wondering how much it would cost to repair it.

- "Wondering" is a continuous form, inappropriate after "looked" without additional words.

Option 2: wondered aligns with the sentence structure and tense.