3. [20 marks] In the following table, the numbers along the top row and left column are node numbers. The numbers inside the main body of the table are the maximal flows along the arcs between the nodes (in the indicated direction). The symbol - means that no flow is possible in the given direction. From / To 1 2 3 4 1 2 13 -- 4 3 7 3 -- 4 8 9 15 a. (5 marks) Draw a picture of the network, showing the flow limitation along the arcs (including the dummy arc). Part (b) continues overleaf b. (15 marks) Write the algebraic model which seeks to maximize the total flow from node 1 to node 4. DO NOT SOLVE THE MODEL.