22. The Cabin Creek Coal (CCC) Company operates three mines in Kentucky and West Virginia, and it supplies coal to four utility power plants along the East Coast. The cost of shipping coal from each mine to each plant, the capacity at each of the three mines, and the demand at each plant are shown in the following table:

Â				Plant	Â
  Mine	  1	  2	Â		  3	  4	Mine Capacity (tons)
1	$7	$9	Â		$10	$12	220
2	9	7	Â		8	12	170
3	11	14	Â		5	7	280
Demand (tons)	110	160	Â		90	180	Â

The cost of mining and processing coal is $62 per ton at mine 1, $67 per ton at mine 2, and

$75 per ton at mine 3. The percentage of ash and sulfur content per ton of coal at each mine is as follows:

Mine	% Ash	% Sulfur
1	9	6
2	5	4
3	4	3

Each plant has different cleaning equipment. Plant 1 requires that the coal it receives have no more than 6% ash and 5% sulfur; plant 2 coal can have no more than 5% ash and sulfur com- bined; plant 3 can have no more than 5% ash and 7% sulfur; and plant 4 can have no more than 6% ash and sulfur combined. CCC wants to determine the amount of coal to produce at each mine and ship to its customers that will minimize its total cost.

1. Formulate a linear programming model for this problem.

2. Solve this model by using the computer.