- Massey Corporation uses a process cost system and the weighted average cost flow assumption Production begins in the Fabricating: Departiment where materials are added at the beginning of the process and conversion costs are incurred uniformil throughout the process, On March 1, the beginning work in process inventory consisted of 20,000 units which were 60% complete and had a cost of $175,000,$145,000 of which were materials costs. During March, the following occurred: Answer the following questions and show the compotations that support your answers (a) What are the equivalent units of production for materials and conversion costs in the Fabricating Departinent for the month of March