Consider the following linear programming problem: maximize 2X1 + X2 + 5X3 - 3X4, Subject to X1 + 2X2 + 4X3 - X4 <= 6 2X1 + 3X2 - X3 + X4 <= 12, X1 + X3 + X4 <= 4, X1, X2, X3, X4 >= 0 a) Find a basic feasible solution with the basic variables X1, X2, and X4 b) Is this solution optimal? If not, then starting with this solution, find the optimal solution by the simplex method.