Answer:
Sunk cost
Step-by-step explanation:
The Sunk Cost is the cost i.e. already incurred and have no impact with respect to the decision making. Also it can be recovered once it is incurred
Since in the given situation the $42 per unit is spend on the defective goods production this represent that is already spent
So, the $42 per unit represent the sunk cost
Hence, the same is relevant