An on-line drug store (ODS) sells 10,000 bottles of vitamins per month. It incurs a fixed order cost of $100 per order, and an annual holding cost of 20%. The manufacturer charges $3.00/bottle, and incurs $2.00/bottle in production, $250/order in shipping and handling, and 20% holding the inventory

1. If the manufacturer offers a 10% discount for a retailer order quantity above 6400, what is the optimal retailer order quantity?