Sarah's Talking Dolls Manufactures a Computer Chip Used in the Production

Sarah's Talking Dolls manufactures a computer chip used in the production of dolls for children.When 5,000 dolls are produced,the costs per part are:

Sam's Associates has offered to sell Sarah's Talking Dolls 5,000 parts for $5.75 each.If Sarah accepts the offer,fixed manufacturing costs will decrease by $1.00 per unit.
A)What is the relevant per unit cost to manufacture the part?
B)Which alternative is best for Sarah's Talking Dolls and by how much?