The Nola Corporation has a standard costing system in which variable snowball manufacturing overhead is assigned to production on the basis of standard machine-hours. Their overhead is all related to their factory expenses. Their factory is at full capacity. The following data are available for July Actual variable snowball manufacturing overhead cost incurred: $12,350 Variable snowball manufacturing overhead rate variance: $2.110 U Actual machine-hours worked: 1,600 hours . Total variable snowball manufacturing overhead spending variance: $2,850 U Total variable snowball manufacturing overhead activity variance: $2,250 U The variable overhead efficiency variance for July is: O $740 F $600 U $600 F 040 0