Department E had 4,000 units in Work in Process that were 40% completed at the beginning of the period at a cost of $12,500. 14,000 units of direct materials were added during the period at a cost of $28,700. 15,000 units were completed during the period, and 3,000 units were 75% completed at the end of the period. All materials are added at the beginning of the process. Direct labor was $32,450 and factory overhead was $18,710. The number of equivalent units of production for the period for materials if the average cost method is used to cost inventories was a. 18,000 b. 17,250 c. 15,650 d. 17,700