Department $M$ had $3,000$ units $51\%$ completed in process at the beginning of June, $13,800$ units completed during June, and $1,626\%$ completed at the end of June. The number of equivalent units of production for conversion costs for June if the first$-$in$,$ first method is used to cost inventories is

a$.14,216$ units

b$.10,800$ units

c$.15,816$ units

d$.12,686$ units