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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 please