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 a mean of $100$ and a standard deviation of $55($measured in boxes$).$ Each week, a replenishment order is placed to the paper factory and the order arrives four weeks later. The demand is already normalized, so there is no need to recalculate the mean and standard deviation for l $+1$ periods. 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.