The Litton Company has established standards as follows: Direct material 3 lbs. @ $4/lb. = $12 per unit Direct labor 2 hrs. @ $8/hr. = $16 per unit Variable manufacturing overhead 2 hrs. @ $5/hr. = $10 per unit Actual production figures for the past year are given below. The company records the materials price variance when materials are purchased. Units produced 600 Direct material used 2,000 lbs. Direct material purchased (3,000 lbs.) $11,400 Direct labor cost (1,100 hrs.) $ 9,240 $ 5,720 Variable manufacturing overhead cost incurred The company applies variable manufacturing overhead to products on the basis of direct labor hours. The variable overhead efficiency variance is: Select one: O a. $520 F. b. $520 U c. $500 U. d. $500 F