Xia Co$.$ currently buys a component part for $$9$ per unit. Xia believes that making the part would require $$4\mathrm{.}35$ per unit of direct materials and $$1\mathrm{.}15$ per unit of direct labor. Xia allocates overhead using a predetermined overhead rate of $230\%$ of direct labor cost. Xia estimates an incremental overhead rate of $$0\mathrm{.}50$ per unit to make the part.

$$

$1-$a$.$ What are the relevant costs for Xia to make or buy the part?

$1-$b$.$ Should Xia make or buy the part?