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

Deleston Boat Wash's cost formula for its cleaning equipment and supplies is $2,150 per month plus $21 per boat. For the month of September, the company planned for activity of 79 boats, but the actual level of activity was 39 boats. The actual cleaning equipment and supplies for the month was $3,110.
-The cleaning equipment and supplies in the flexible budget for September would be closest to:

A) $1,880
B) $3,110
C) $3,809
D) $2,969