Refer to Problem 17. Suppose that shipments between the two

Refer to Problem 17. Suppose that shipments between the two warehouses are permitted at $2 per unit and that direct shipments can be made from plant 3 to customer 4 at a cost of $7 per unit. ,a. Develop a network representation of this problem.,b. Formulate a linear programming model of this problem.,c. Solve the linear program to determine the optimal shipping plan.