It's probably really easy I'm just really dumb

Rearrange the formula c^2 = a^2 + b^2 for b

Marco has $38.43 dollars in his checking account. his checking account is linked to his amazon music account so he can buy music. the songs he purchases cost $1.29. part 1: write an expression to describe the amount of money in his checking account in relationship to the number of songs he purchases. part 2: describe what the variable represents in this situation.

Which is f(5) for the function –2x2 + 2x - 3?