Weekly demand for DVD-Rs at a retailer is normally distributed with a mean of 1,000 boxes and a standard deviation of 150. Currently, the store places orders to the supplier, with a reorder point of 4,200 boxes. The order quantity to the supplier is fixed at 5,000 boxes. Replenishment lead time is 4 weeks, fixed order cost per order is $100, each box costs the retailer $10, and the inventory holding cost is 25% per year. Assume 50 weeks in a year. Given the problem parameters, what is the optimal order quantity the retailer should order?