The debits to Work in Process-Assembly Department for May, together with data concerning production, are as follows: May 1, work in process: Materials cost, 3,000 units $8,000 Conversion costs, 3,000 units, 66.7% completed 6,000 Materials added during May, 10,000 units 30,000 Conversion costs during May 31,000 Goods finished during May, 11,500 units 0 0 May 31 work in process, 1,500 units, 50% completed All direct materials are placed in process at the beginning of the process and the first-in, first-out method is used to cost inventories. The materials cost per equivalent unit for May is a. $3.80 Ob. $3.00 Oc. $2.31 d. $2.92