Q16.3*(Quick Print) Quick Print Inc. uses plain and three-hole-punched paper for copying needs. Demand for each paper type is highly variable. Weekly demand for the plain paper is estimated to be normally distributed with mean 100 and standard deviation 65 (measured in boxes). Each week, a replenishment order is placed to the paper factory and the order arrives five weeks later. All copying orders that cannot be satisfied immediately due to the lack of paper are back-ordered. The inventory holding cost is about $1 per box per year.

What is Quick Print's optimal order-up-to level for plain paper if Quick Print operates with a 99 percent in-stock probability?

I think this is the formula I am supposed to use but I am not sure how...S = + z . I need step by step please.