For a product satisfying Economic Order Quantity (EOQ) model assumptions, the annual demand is 9000 units, the purchase cost is $40/unit and the inventory holding cost per unit per year is 20% of the purchase cost. The ordering cost is $300 per order.

Question: Calculate the economic order quantity (optimal order quantity) to minimize the annual inventory cost, based on the information above and then round off optimal Q₀ to the closest multiple of 10 (for practical purposes).