Harris Enterprises machines heavy-duty brake rotors that are used on commercial airliners. The company's management developed the following standard costs: Standard direct labor hours per rotor Standard overhead rate per direct labor hour 2.3 $8.25 Actual activity for October: Actual overhead costs incurred Actual direct labor hours Actual rotors machined $117,000 11,700 3,800 What is the variable manufacturing overhead efficiency variance in October? OA. $20,475 unfavorable c OB. $24,420 unfavorable OC. $24,420 favorable OD. $20,475 favorable