The Ace Battery Company has forecast its sales in units as follows: January 900 May 1,450 February 750 June 1,600 March 700 July 1,300 April 1,200 Ace always keeps an ending inventory equal to 110 percent of the next month's expected sales. The ending inventory for December (January's beginning inventory) is 990 units, which is consistent with this policy. Materials cost $10 per unit and are paid for in the month after production. Labour cost is $3 per unit and is paid in the month the cost is incurred. Overhead costs are $6,500 per month