A supplier of components for a retail computer supply store has established the following discount schedule: QUANTITY PRICE/UNIT 1-499 units $5.00 500-999 units $4.50 1000 or more units $3.90 Ordering cost per order is $20, holding cost is quoted as 20% of the cost we pay for each item, and annual demand for this particular model is estimated to be 10000 units. Determine the optimal size of the order for the retail computer supply store.