13. The tableau given below corresponds to a maximization problem in decision variables x; 0 (j = 1, 2, . . ., 5): Basic Current variables values X1 X2 X3 X4 X5 X3 4 -1 1 x4 1 a2 -4 1 X5 b 3 1 (-z) -10 C -2 State conditions on all five unknowns a1, a2, a3, b, and c, such that the following statements are true. a) The current solution is optimal. There are multiple optimal solutions. b) The problem is unbounded. c) The problem is infeasible. d) The current solution is not optimal (assume that b > 0). Indicate the variable that enters the basis, the variable that leaves the basis, and what the total change in profit would be for one iteration of the simplex method for all values of the unknowns that are not optimal.