Opal Production Company uses a standard costing system. The following information pertains to the current year: Actual factory overhead costs ($15,000 is fixed) $50,000 Actual direct labor costs (10,000 hours) $130,000 Standard direct labor for 6,000 units: Standard hours allowed 9,500 hours Labor rate $10.00 The factory overhead rate is based on an activity level of 12,000 hours. Standard cost data for 6,000 units is as follows: Variable factory overhead $18,000 Fixed factory overhead 12,000 Total factory overhead $30,000 What is the variable overhead efficiency variance for Opal Production Company? a.$540 F b.$820 F c.$750 U d.$980 U