The Aliena Corporation buys automotive equipment for $1,800 and sells it for $2,500; the company has the following sales forecast: 100 units for October, 120 units in November, 200 units in December and 400 units in January. Ending inventory for each month should be 10% of the next month's sales. The company had 20 units on hand at September 30th. How many units should be purchased in November?