Solve the given linear programming problem using the simplex method. If no optimal solution exists, indicate whether the feasible region is empty or the objective function is unbounded. (Enter EMPTY if the feasible region is empty and UNBOUNDED if the objective function is unbounded.) Maximize  p = x + y + 2z  subject to x  +  2y  +  2z  ≤  20 2x  +  y  +  3z ≤ 20 x  +  3y  +  6z ≤ 20 x ≥ 0, y ≥ 0, z ≥ 0.