B.
Explanation: the $0.50 is multiplied by the number of customers(“plus $.50 for each customer on her paper route”). So, it can’t be A, because the $0.50 is not in the equation. It can’t be c, because there should not be $2 for the number of customers(x). It can’t be D either because it’s 0.50, not 50. So, you’re left with B.