Henrique​ Correa's bakery prepares all its cakes between 4 A.M.and 6 A.M.so they will be fresh when customers arrive.​ Day-old cakes are virtually always​ sold, but at a​ 50% discount off the regular ​$8 price. The cost of baking a cake is ​$5​, and demand is estimated to be normally​ distributed, with a mean of 20 and a standard deviation of 7. What is the optimal stocking​ level?