During $2021,$ it cost Coronado Inc. $$12$ per unit to produce Part T$5.$ During $2022,$ the cost has increased

to $$14$ per unit. In $2022,$ Sandhill Company has offered to sell the Part T$5$ for $$8$ per unit to Coronado.

With regard to the make$-$or$-$buy decision, which statement is true?

Incremental costs are $$4$ per unit.

Incremental revenues are $$2$ per unit.

Net relevant costs are $$4$ per unit.

Differential costs are $$6$ per unit.