Bruce corporation makes four products in a single facility. these products have the following unit product costs: products a b c d direct materials $ 19.90 $ 15.20 $ 20.80 $ 23.20 direct labor 12.20 8.70 10.50 7.40 variable manufacturing overhead 1.60 2.10 2.00 2.10 fixed manufacturing overhead 10.80 11.90 8.80 10.70 unit product cost $ 44.50 $ 37.90 $ 42.10 $ 43.40 additional data concerning these products are listed below. products a b c d grinding minutes per unit 1.20 0.70 0.60 0.60 selling price per unit $ 59.30 $ 51.70 $ 59.50 $ 55.60 variable selling cost per unit $ 3.60 $ 1.50 $ 2.20 $ 3.60 monthly demand in units 4,000 2,000 4,000 2,000 the grinding machines are potentially the constraint in the production facility. a total of 9,800 minutes are available per month on these machines. direct labor is a variable cost in this company. how many minutes of grinding machine time would be required to satisfy demand for all four products? 10,800 9,800 10,500 12,000