Suppose that the general solution of a system of three equations in three variables is (x, y, z) = (x, x + 1, 6). Which of the following triples is a solution of the system? (a) (3, 2, 6). (b) (3, 5, 6). (c) (4, 3, 6). (d) (4, 5, 6). (e) None of these.