To make a batch of 1,000 units of a certain item, it is estimated that 120 direct labor hours are required at a cost of \($10/hour.\) Direct material costs are estimated at \($1,500\) per batch. The overhead costs are calculated based on an overhead rate of \($7.50\) per direct labor hour. The item can be readily purchased from a local vendor for \($4\) per unit.

a. Should the item be made or purchased?

b. Over what range of overhead rate is your answer in Part a valid?