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 $9,000 Conversion costs, 3,000 units, 50% completed 5,900 Materials added during May, 10,000 units 27,100 Conversion costs during May 33, 100 Goods finished during May, 11,500 units May 31 work in process, 1,500 units, 50% completed 0 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 0 a. $2.71 b. $2.36 c. $3.31 d. $4.21