Coalco produces coal at three mines and ships it to four customers. The cost per ton of producing coal, the ash and sulfur content (per ton) of the coal, and the production capacity (in tons) for each mine are given in the file P04_57.xlsx. The number of tons of coal demanded by each customer and the cost (in dollars)

of shipping a ton of coal from a mine to each customer are also provided in this same file. The amount of coal shipped to each customer must contain at most 6% ash and at most 3.5% sulfur.

Show Coalco how to minimize the cost of meeting customer demands.