Hello can someone take a look at this. It from cengage 27th edition. thank you

Department R had 4,200 units in work in process that were 77% completed as to labor and overhead at the beginning of the period. During the period, 33,700 units of direct materials were added, 35,700 units were completed, and 2,200 units were 28% completed as to labor and overhead at the end of the period. All materials are added at the beginning of the process. The first-in, first-out method is used to cost inventories. The number of equivalent units of production for conversion costs for the period was

a.37,282

b.33,082

c.35,700

d.42,100

I think work it out to an answer of C. but you think? thank