The first three equations uniquely determine x=−11/5, y=19/5, z=7/5 (solve y from eq.1, substitute into eq.3 to get z in terms of x, then substitute both into eq.2). Checking the fourth equation with these values: −11/5 − 2(19/5) + 7(7/5) = (−11−38+49)/5 = 0, exactly matching its right-hand side — so the fourth equation is consistent with (not independent of) the first three, and the system has exactly 1 solution.