Question $3.$ A shop stocks a high$-$volume item that has a normally distributed demand during lead time. The expected demand during lead time is $500$ units, and the standard deviation of demand during lead time is $25.$

a$)$ What should the reorder point that limits the probability of stockout to $5\%?$ Also, write the Excel formula for this problem below.

b$)$ How much must be the safety stock?