Rocky Mountain Tire Center sells 20,000 go-cart tires per year. The ordering cost for each order is $40,and the holding cost percentage is 20% of the purchasing price of the tires per unit per year. The purchasing price is $20 per tire if fewer than 500 tires are ordered, $18 per tire if 500 or more - butfewer than 1,000 - tires are ordered, and $17 per tire if 1,000 or more tires are ordered. How manytires should Rocky Mountain order each time it places an order, and what is the minimum total cost?