Cox Engineering performs cement core tests in its laboratory. Variable manufacturing overhead is assigned to core tests on the basis of standard direct labor hours. The following standards for variable manufacturing overhead have been set for each core test performed:

Standard variable manufacturing overhead rate ........................................ $8 per direct labor hour

Standard direct labor hours ............................................................................. 0.4 direct labor hours per test performed

The information for July is as follows:

Actual number of tests performed ............................................................ 1,800 tests performed

Actual direct labor hours worked.................................................................. 860 direct labor hours

Actual variable manufacturing overhead incurred .................................. $3,200

The variable overhead efficiency variance for July is:

$960 unfavorable

$640 unfavorable

$1,120 unfavorable

$800 unfavorable