this answer that already exist is wrong, please someone answer it.
Modeling (questions a, b and c are independent)
a. Assuming that x1, x2, x3 and x4 ? [?4, 4], propose and justify constraints, by introdu- cing additional variables if necessary, to guarantee each of the following conditions: i. u = 1 =? 3x1 ? 3x2 ? 2x3 + 7x4 = 55.
ii. u = 0 =? 6x1 + 7x2 ? 2x3 + 2x4 ? 78.
b. Assuming that u1, u2, u3 and u4 ? {0, 1}, propose and justify one or more several cuts (valid inequalities) of knapsack type for the inequalities below, and only keep the dominant cuts: 10u1 + 6u2 + 12u3 + 7u4 ? 20.
c. Explain and justify the impact of adding cuts (also called valid inequalities) in an Integer Linear Program (P) on its resolution using a standard solver