A retailer sells an excellent grape soda. She buys the soda from a supplier and incurs a setup charge of $10 each time she orders. Demand for the soda is 4000 cases per year, and holding cost are 2$ per case per year. The purchase price per case is $5.00 for 1-100, $4.80 for 101-400, and $4.60 for any order over 401 cases. What is her optimal order quantity to minimize total cost?