Minimum cost Hard brick, Inc, has two kilns, Kiln I can produce 3000 grey bricks, 2000 red bricks, and 300 glazed bricks daily. For Kiln II the corresponding figures are 2000, 5000 and 1500. Daily operating costs of Kilns I and II are $400 and $ 600, respectively. Find the number of days of operation of each kiln so that the operation cost in filling an order of 18000 grey, 34000 red, and 9000 glazed bricks is minimized.