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: . Actual variable manufacturing overhead cost incurred: $26,800 . Actual machine-hours worked: 3,500 hours . Variable overhead rate variance: $6,270 U . Total variable overhead spending variance: $8,800 U The variable overhead efficiency variance for July is