=b. This problem is only a variant of a minimum-cost flow problem because the supply from each vendor is a maximum of 10 rather than a fixed amount of 10. However, it can be converted to a full-fledged minimum-cost flow problem by adding a dummy demand node that receives (at zero cost) all the unused supply capacity at the vendors. Formulate a network model for this minimum-cost flow problem by inserting all the necessary data into the network drawn in part a supplemented by this dummy demand node. (Use the format depicted in Figure