The following questions refer to a capital budgeting problem with six projects represented by 0-1 variables x 1, x2, x 3, X4, X5, and x 6: a. Write a constraint modeling a situation in which two of the projects 1, 3, 4 and 5 must be undertaken. For those boxes in which you must enter subtractive or negative numbers use a minus sign. (Example: -300) x1 + x3+ x4 + b. Write a constraint modeling a situation in which, if projects 3 and 5 must be undertaken, they must be undertaken simultaneously. For those boxes in which you must enter subtractive or negative numbers use a minus sign. (Example: -300) x3 + c. Write a constraint modeling a situation in which project 1 or 6 must be undertaken, but not both. For those boxes in which you must enter subtractive or negative numbers use a minus sign. (Example: -300) x1 + X6 d. Write constraints modeling a situation where project 6 cannot be undertaken unless projects 1 and 3 also are undertaken. For those boxes in which you must enter subtractive or negative numbers use a minus sign. (Example: -300) X6 X6 x1 x3 e. Write constraints modeling a situation where project 6 cannot be undertaken unless projects 1 and 3 also are undertaken. Assume that when projects 1 and 3 are undertaken, project 6 also must be undertaken. For those boxes in which you must enter subtractive or negative numbers use a minus sign. (Example: -300) X6 X6 x1 X3 X6 x1 + x3+