The Following Standards for Variable Manufacturing Overhead Have Been Established

The following standards for variable manufacturing overhead have been established for a company that makes only one product: $\begin{array}{lccc}\text {Standard hours per unit of output}&\text {7.8 hours}\\\text {Standard variable overhead rate}&\text { \$ 12.55 per hour}\\\end{array}$
The following data pertain to operations for the last month: $\begin{array} { l r } \text { Actual hours } & 2,900 \text { hours } \\\text { Actual total variable overhead cost } & \$ 36,975 \\\text { Actual output } & 200 \text { units }\end{array}$ What was the variable overhead efficiency variance for the month?

A) $0.
B) $16,817 unfavourable.
C) $580 unfavourable.
D) $17,397 unfavourable.