Answer:
In this case, the differential cost os $18.
Step-by-step explanation:
The differential cost is the increase in unitary or total production value in two or more steps of the decision-making process. In this case, the unitary cost of product B is not a differential cost. It would remain constant in both products, but, the additional $18 is a cost incurred only in product C.
In this case, the differential cost os $18.