The Maxit Corporation Has a Standard Costing System in Which $\bullet$

The Maxit Corporation has a standard costing system in which variable manufacturing overhead is assigned to production on the basis of standard machine-hours. The following data are available for July: $\bullet$ Actual variable manufacturing overhead cost incurred: $11,310
$\bullet$ Actual machine-hours worked: 1,600 hours
$\bullet$ Variable overhead rate variance: $1,710 U
$\bullet$ Total variable overhead spending variance: $2,310 U
The variable overhead efficiency variance for July is:

A) $600 U
B) $540 U
C) $540 F
D) $600 F