Pratte Boat Wash's Cost Formula for Its Cleaning Equipment and Supplies

Pratte Boat Wash's cost formula for its cleaning equipment and supplies is $2,460 per month plus $49 per boat. For the month of April, the company planned for activity of 58 boats, but the actual level of activity was 18 boats. The actual cleaning equipment and supplies for the month was $3,470.
Why such a great disparity between the planned and actual level of activity from 58 to 18 boats - should these be closer together?
Please keep as is. Such a large discrepancy is ok.
-The spending variance for cleaning equipment and supplies in April would be closest to:

A) $1,832 U
B) $128 F
C) $128 U
D) $1,832 F