The cost to produce Part A was $20 per unit in 2016. During 2017, it has increased to $23 per unit. In 2017, Supplier Company has offered to supply Part A for $18 per unit. For the make or buy decision:

a. Incremental revenues are $5 per unit

b.Incremental costs are $3 per unit

c.Net relevant costs are $3 per unit

d.Differential costs are $5 per unit

How do I solve this??

Thank you