5-10. In Problem 5-8, suppose that the daily demand at area 3 drops to 4 million gallons.  Surplus production at refineries 1 and 2 is diverted to other distribution areas by truck. The transportation cost per 100 gallons is $1.50 from refinery 1 and $2.20 from refinery 2. Refinery 3 can divert its surplus production to other chemical processes within the plant.  (a) Construct the associated transportation model.  (b) Determine the optimum shipping schedule in the network.  TABLE 5.26 Mileage Chart for Problem 5-8  Distribution area  2  180  800  200  1  180  300  220  3  Refinery 1  Refinery 2  Refinery 3  900  120