The question i below, need help with parts b, c, and d

Consider an undirected network shown in the following gure, where numbers along the arcs (1', j) represent distances between nodes i and j. Assume that the distance from i to j is the same as from j to t (i.e., all arcs are two-way streets). Please note that you do not need to use EXCEL to solve this question. a) Develop a binary integer programing model that can be used to nd the minimum distance required to make a delivery from node 1 to node 6. {It} marks) 13) Suppose that you use EXCEL to solve the integer programming in part a) and nd a shortest route as 1 4 5 6. How to add one more constraint to the formulation in part a) to determine whether there is a different shortest route or not? [2 marks) c) It is sometimes crucial to have a backup route between two nodes in certain circumstance. [n the event there are additional constraints or there is some road closed, the second shortest route might be used. Ifthe shortest route 1 4 5 6 for this problem is unique, how to add one more constraint to the formulation in part a) to determine the second shortest route?I Use two different approaches. (4 marks) d) Suppose that road between nodes 2 and 3 is closed for annual maintenance on both directions. Use two different ways to modify the formulation in part a) to reect this new information. (4 marks)