Furniture Inc. manufactures mattresses. The estimated number of mattresses for the first three months of 2020 is as follows: Month Sales units January 5,000 February 7,000 March 6,500 Finished goods inventory on 31 December 2019 is 1,500 units. Ending finished goods are equal to 30% of next month's sales. April sales are expected to total 8,000 units. How many mattresses will be produced in the first quarter of 2020?