Now, consider Exercise 13 with a marginal unit quantity discount.

Demand for fasteners at W.W. Grainger is 20,000 boxes per month.

The holding cost at Grainger is 20 percent per year. Each order incurs a fixed cost of $400. The supplier offers a marginal unit discount pricing scheme with a price of $5 per box for the first 30,000 and a price of $4.90 per unit for each unit above 30,000 in an order. How many boxes should Grainger order per replenishment?