The debits to Work in Process-Assembly Department for April, together with data concerning production are as follows: April 1, work in process Materials cost, 3000 units $8000 Conversion costs, 3000 units 66.7% complete $6000 Materials added during April, 10,000 units $30,000 Covension cost during April $31,000 Goods finished during April, 11,500 units -April 30 work in process, 1,500 units, 50% complete 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 April is: a. 3.00 b. 3.80 c. 2.92 d. 2.31.