1. Consider the minimum cost flow problem shown below, where the bi values (net flows generated) are given by the nodes, the cij values (costs per unit flow) are given by the arcs, and the uij values (arc capacities) are given between nodes C and D. (a) Now consider the following BF solution: Basic variables: xAB=15,xAD=5,xCE=25,xDE=5; Nonbasic variables: xAC=0,xBC=25,xBD=0. Use the optimality test to verify that this BF solution is optimal. What is the total cost of the optimal solution? (b) When you did the optimality test in part (a), what tells you that there are multiple optimal solutions (hint: pay attention to the Z value)? Find another optimal solution