6. 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 there are no upper bounds (arc capacities) are given. a) Obtain an initial BF solution by solving the feasible spanning tree with basic arcs A B,BC,CD. b) Find an optimal basic feasible spanning tree and the corresponding optimal solution using this initial BF solution and its optimal cost