Demand for walnut fudge ice cream at the Sweet Cream Dairy can be approximated by a normal distribution with a mean of 20 gallons per week and a standard deviation of 5 gallons per week. The new manager desires a service level of 90 percent. Lead time is 7 days, and the dairy is open seven days a week. If the ROP model is used, what is the appropriate safety stock level to achieve the desired service level? Round to two decimal places. (Hint: Work in terms of days or weeks?)