Department $M$ had $2,100$ units $54\%$ completed in process at the beginning of June, $14,000$ units completed during June, and $1,800$ units $34\%$ completed at the end of June. The number of equivalent units of production for

conversion costs for June if the first$-$in$,$ first$-$out method is used to cost inventories is

a$.16,412$ units

b$.13,478$ units

c$.14,612$ units

d$.11,900$ units