A burger restaurant buys top-grade ground beef for $3 per kg. A large sign over the entrance guarantees that the meat is fresh daily. Any leftover meat is sold to the local high school cafeteria for $2 per kg. Eight hamburgers can be prepared from each kilogram of meat. Burgers sell for $2 each. Labour, overhead, meat, buns, and condiments cost $l per burger. Demand for ground beef is Normally distributed with a mean of 400 kg per day and a standard deviation of 50 kg per day. What daily order quantity' is optimal?