how do you solve this?

A new logistics analyst has approached you regarding a potential problem. Her analysis indicates the cost of a back order is $70 for our Autographed Footballs, but she is not sure what the appropriate safety stock should be. Given this back order cost, what probability of a stock cis winuld be appropriate to use to manage the inventory levels? Standard Deviation of Forecasted Vemariu uurng Lead Time 20 10% 5% 4% 1%