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 $8,300 Conversion costs, 3,000 units, 66.7 % completed 5,500 Materials added during May, 10,000 units 27,100 Conversion costs during May 33,900 Goods finished during May, 11,500 units 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 Oa. $4.22 Ob. $3.39 Oc. $2.71 Od. $2.36