Demand for walnut fudge ice cream at the Sweet Cream Dairy can be approximated by a normal distribution with a mean of 21 gallons per week and a standard deviation of 3.5 gallons per week. Lead time is two days, and the dairy is open seven days a week.

If a fixed-interval model with an order interval of 10 days is used, what order size would be needed for a 98 percent service level and a supply of 8 gallons on hand at the order time? ( Hint: Work in terms of weeks.)