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

Standard hours per unit of output	6.4	hours
Standard variable overhead rate	$12.80	per hour

The following data pertain to operations for the last month:

Actual hours	2,650	hours
Actual total variable manufacturing overhead cost	$34,570
Actual output	150	units

What is the variable overhead efficiency variance for the month?

$21,632 U

$22,282 U

$12,288 F

$650 F