= Annual demand for a particular halogen bulb is D = 3,600 at a business that operates 300 days per year. The cost per order S = $25 and the holding cost per unit per year is $2. If the lead time is 5 days, and demand during lead time follows the empirical distribution given in the following table: Number of Units Probability 30 .10 40 .10 50 .15 60 .30 70 .15 80 .10 90 .10 What level of safety stock is required to ensure a 90% service level? Select one: O a. 20 O b. 30 O c. 40 O d. 50 O e. 60