Areas Covered Potential Locations for Substations A B D E F G 1, 5, 7 1, 2, 5, 7 1, 3, 5 2, 4, 5 3, 4, 6 4, 5, 6 1, 5, 6, 7 2. Integer programming formulation: The following questions refer to a capital budgeting problem with six projects represented by 0-1 variables X1, X2, X3, X4, X5, and x6: a. Write a constraint modeling a situation in which two of the projects 1, 3, 5, and 6 must be undertaken. b. Write a constraint modeling a situation in which, if projects 3 and 5 must be undertaken, they must be undertaken simultaneously. Write a constraint modeling a situation in which project 1 or 4 must be undertaken, but not both. d. Write constraints modeling a situation where project 4 cannot be undertaken unless projects 1 and 3 also are undertaken. In addition to the requirement in part (d), assume that when projects 1 and 3 are undertaken, project 4 also must be undertaken