Consider the objective function z = Ax + By (A > 0 and B > 0) subject to the following constraints: 2x + 3y ≤ 9, x - y ≤ 2, x ≥ 0, and y ≥ 0. Prove that the objective function will have the same maximum value at the vertices (3, 1) and (0, 3) if A = 2/3 B.