Steve's gym is expanding their services and offering shakes for their patrons to purchase as workout recovery. He anticipates a daily demand of 70 shakes, plans to offer them every day (they are closed for 7 holidays a year). To have all his supplies delivered, it costs him $15 per order. His carrying costs are $0.50 per shake per year. What is the optimal number of supplies for shakes should he order? Please show work.