which equation represents the cost?

Question

Carson decided to participate in an online download movie program. It costs $45 to join. The $45 includes the membership fee and 15 free downloads. She will pay $1.15 for each additional download. What equation represents the cost?

A. C = 1.15(x - 15) - 45

B.C = 1.15(x - 15) + 45

C. C = (1.15x + 15) + 45

D. C = 1.15x + 45

Answer 1

45 is the fixed cost, so that eliminates A

C is charging for the 15 free downloads, so that eliminates C

Correct answer is either B or D. D would be correct if x = any downloads over 15

B would be correct if x>14. but if x=14 or less, it's false, since there is no discount for using less than 15 downloads.

D seems to be the better answer, if you interpret x as being the number of downloads over 15

But my guess is they probably want B as the correct answer since it explicitly uses 15 while D never mentions it.

It's ambiguous. While I suspect D is the better answer, odds are the tester wants B as the correct answer