3. Transshipment Model (10 points) This is an extension of the transportation model. There are now intermediate transshipment points added between the sources (plants) and destinations (retailers). Items being shipped from a Plant (p) must be shipped to a Warehouse (w) before being shipped to the Retailer (r) Each Plant will have an associated supply (s) and each Retailer will have a demand (d). The number of plants is n, number of warehouses is q and the number of retailers is m. The edges (i.j) from plant (p)to warehouse (w) have costs associated denoted cpli.j). The edges (j.k) from a warehouse (w)to a retailer (r) have costs associated denoted cw(j,k). The graph below shows the transshipment map for a manufacturer of refrigerators. Refrigerators are produced at four plants and then shipped to a warehouse (weekly) before going to the retailer. R2 P1 R3 P2 W2 R4 P3 R5 P4 R6 R7 Below are the costs of shipping from a plant to a warehouse and then a warehouse to a retailer. If it is impossible to ship between the two locations an X is placed in the table