4. Multi-Source Max-Flow. (10 points) Consider a variant of the max-flow problem where, instead of having just a single source s, the input graph G = (V, E) now has k sources 81, 82, ..., 84. Thus, the value of the flow is redefined to be the sum of the flows leaving all sources (SI = El-Evev f(s,v). Explain how you can transform graph G into another graph G' that has a single source and show how a max-flow solution to G' can be translated into a max-flow solution to the multi-source G. (Hint: recall that we did something similar for the bipartite matching problem), 3