A company sells 3,600 electric motors each year. The cost of these is $200 each, and demand is constant throughout the year. The cost of placing an order is $40, while the holding cost is $20 per unit per year. There are 360 working days per year and the lead-time is 5 days. If the company orders 200 units each time he places an order, what would his average inventory be (in units)?