Inventory Management $($Quantity Discount Model:$$Dell Computers purchases integrated chips at $$350$ per chip. The holding cost is $$35$ per unit per year, the ordering cost is $$120$ per order, and sales are steady, at $400$ per month. The companys supplier, Rich Blue Chip Manufacturing, Inc., decides to offer price concessions in order to attract larger orders. The price structure is shown below. a$)$ What is the optimal order quantity and the minimum annual cost for Bell Computers to order, purchase, and hold these integrated chips? b$)$ Bell Computers wishes to use a $10\%$ holding cost rather than the fixed $$35$ holding cost in $($a$).$ What is the optimal order quantity, and what is the optimal annual cost?