An airline has p flight legs that it wishes to service by the fewest possible planes. to do so, it must determine the most efficient way to combine these legs into flight schedules. the start time for flight i is ai and the finishing time is bi . the plane requires rij hours to return from the point of destination of flight i to the point of origin of flight j. formulate this as a network flow problem. you should clearly state how to construct the network from the given data, and justify that your formulation correctly models the problem