Demand for an item is Normally distributed with a mean of 400 units a week and a standard deviation of 60 units. Ordering and delivery cost $300, holding cost is $12 a unit a year and lead time is constant at 3 weeks. Describe an ordering policy that gives a 95 per cent cycle-service level. What is the cost of holding the safety stock in this case? How much would costs rise if the service level is raised to 98 per cent?