The Midlands Field Produce Company contracts with Potato farmers in Colorado, Minnesota, and North Dakota for monthly potato shipments. Midlands picks up the potatoes at the farms and ships mostly by truck (and sometimes by rail) to its sorting and distribution centers in Ohio and Missouri. At these centers the potatoes are cleaned, rejects are discarded, and the potatoes are sorted according to size and quality. They are then shipped to combination plants and distribution centers in Virginia, Pennsylvania, and Georgia, where the company produces a variety of potato products and distributes bags of potatoes to stores. There is one exception. The Ohio distribution center will not accept potatoes from Colorado because of disagreements over delivery schedules and quality issues. Following are summaries of the shipping costs from the farms to the distribution centers and the processing and shipping costs from the distribution centers to the plants, as well as the available monthly supply at each farm, the processing capacity at the distribution centers, and the final demand at the plants (in bushels):

	Distribution Center ($/bushel)
Farm	4. Ohio	5. Missouri	Supply (bushels)
1. Colorado	$-	$1.09	1,600
2. Minnesota	0.89	1.32	1,100
3. North Dakota	0.78	1.22	1,400
Processing Capacity (bushels)	1,400	2,500
	Plant ($/bushel)
Distribution Center	6. Virginia	7. Pennsylvania	8. Georgia
4. Ohio	$4.56	$3.98	$4.94
5. Missouri	3.43	5.74	4.65
Demand (bushels)	1,200	900	1,100

Formulate a linear programming model to determine the optimal monthly shipments from the farms to the distribution centers and from the distribution centers to the plants to minimize total shipping and processing costs. DO NOT SOLVE THE MODEL.