The following standards for variable manufacturing overhead have been established for a company that makes only one product:

Standard hours per unit of output 5.2 hours
Standard variable overhead rate $11.60 per hour
The following data pertain to operations for the last month:
Actual hours 2,500 hours
Actual total variable manufacturing overhead cost $29,590
Actual output 150 units

What is the variable overhead efficiency variance for the month?

breakdown of calculation