$5.)$ R$.$ C$.$ Barker makes purchasing decisions for his company. One product that he buys costs $$50$ per unit when the order quantity is less than $500.$ When the quantity ordered is $500$ or more, the price per unit drops to $$48.$ The ordering cost is $$30$ per order and the annual demand is $7,500$ units. The holding cost is $10$ percent of the purchase cost. How many units should R$.$ C$.$ order to minimize his total annual inventory hat$(Q)st?$