Please help me, and please explain how you get to the answer.

Your answer is C) 2a² + 2b²
To find this we can just expand the brackets of (a - b)² and (a + b)², and then combine like terms:
(a - b)² = (a - b)(a - b) = a² - 2ab + b²
(a + b)² = (a + b)(a + b) = a² + 2ab + b²
Then when you combine like terms, you get (a² + a²) + (-2ab + 2ab) + (b² + b²), so the ab terms cancel out and you get left with 2a² + 2b².
I hope this helps!