4. (20) A retail store sells television. The television costs $500 to the store and it is sold for $750. Monthly demand can be assumed normal distribution with mean 250 and standard deviation 75. The financial department of the company recommends using 24% annual interest charge to estimate the inventory carrying cost. The order setup cost is negligible and the lead time is zero. a) Suppose the retail store orders periodically once a month and all unfulfilled orders are backordered. The backorder cost is estimated to be $40/unit/month. What order-up-to level should the store use? b) If the store orders periodically once a month and any orders unfulfilled immediately are lost, what order-up-to level should the store use? c) Suppose now the store uses the (Q, r) model. All unfulfilled orders are backordered with unit backorder cost = $50/year, the lead time is 1 month, and the order setup cost is $1. What is the optimal reorder point and reorder quantity