$33)$ Lewis S$.$ Gray Inc. manufactures a part for use in its production of art deco furniture. When $10,000$ items are produced, the costs per unit are:

Direct materials $ $15$

Direct manufacturing labor $60$

Variable manufacturing overhead $25$

Fixed manufacturing overhead $32$

Total $$132$

Colonial Accents Company has offered to sell to Lewis S$.$ Gray $10,000$ units of the part for $$125$ per unit. The plant facilities could be used to manufacture another part at a savings of $$180,000$ if Lewis S$.$ Gray accepts the supplier's offer. In addition, $$30$ per unit of fixed manufacturing overhead on the original part would be eliminated.

Required:

a$.$ What is the relevant per unit cost for the original part?

b$.$ Which alternative is best for Lewis S$.$ Gray Company? By how much?