The manager at Goodstone Tires, a distributor of tires in Illinois, uses a continuous review policy to manage their inventory. The manager currently orders $10,000$ tires when the inventory of tires drops to $6,000.$ Weekly demand for tires is normally distributed with a mean of $2,000$ and a standard deviation of $500.$ The replenishment lead time for tires is two weeks. Each tire costs Goodstone $$40$ and the company sells each tire for $$80.$ Goodstone incurs a holding cost of $25$ percent of the purchasing cost.