Answer:
a.
Relevant costs:
Supplies costs
Inspection costs
Assembly costs
Irrelevant cost:
power cost
b.$20,000
Step-by-step explanation:
The following costs are relevant because they would be incurred as a result of investing in either of the two alternatives:
Supplies costs
Inspection costs
Assembly costs
Power costs is not relevant because is not incurred as direct consequence of the two alternatives,even when none of the alternatives is chosen power cost would still be incurred.
Costs of alternative M=$77,000+$49,000+$42,000+$168000
Costs of alternative N=$68,000+$49,000+$31,000=$148,000
Differential cost=$168,000-$148,000=$20,000