Under the first$-$in$,$ first$-$out costing method:

a$.$ it is assumed that units in beginning work$-$in$-$process are completed first, before any new units are started.

b$.$ equivalent units of work in beginning work$-$in$-$process are counted as part of the total equivalent units.

c$.$ the costs in beginning work$-$in$-$process from the prior period are included in calculating the unit cost.

d$.$ the quantity of in beginning work$-$in$-$process is considered only for calculating the unit cost of the output.