Question: 18. It takes approximately 8 working days for an order of number 6 screws to arrive once the order has been placed. (Refer to Problem 6.17) The demand for number 6 screws is fairly constant, and on the average, Lila has observed that her brother's hardware store sells 500 of these screws each day. Because the demand is fairly constant, Lila believes that she can avoid stock-outs completely if she only orders the number 6 screws at the correct time. What is the ROP?