Cranium, Inc., purchases term papers from an overseas supplier under a continuous review system. The average demand for a popular mode is 300 units a day with a standard deviation of 30 units a day. It costs $60 to process each order and there is a five-day lead-time. The holding cost for a paper is $0.25 per year and the company policy is to maintain a 98% service level. Cranium operates 200 days per year.
What combination of changes in lead-time and service level would result in exactly the same level of safety stock as indicated in the table? ( Please show me the steps how to solve it - i know the answer but i don't know how to solve it)
A) Lead-time drops to 41 days and service level increases to 99%.
B) Lead-time increases to 18.52 days and service level drops to 92%.
C) Lead-time increases to 20.54 days and service level drops to 90%.
D) Lead-time drops to 3.5 days and service level increases to 99.54%.