Tannwin Co. sells a new product called Accountomatic and has predicted the following sales for the first four months of the current year: sales in units: jan-1700 feb-1900 march-2100 april- 1600 Ending inventory for each month should be 20% of the next month's sales, and the December 31 inventory is consistent with that policy. How many units should be purchased in the first quarter of the year?