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 Conversion costs, 3,000 units, 50% completed Materials added during May, 10,000 units Conversion costs during May Goods finished during May, 11,500 units May 31 work in process, 1,500 units, 50% completed $8,400 5,000 25,500 33,800 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 ) Oa. $3.38 b. $2.55 $2.22 d. $4.22