Ada yang bisa nomor 3? tolong dong

2x + 4y – z = 12
-2x +2y + 4z = -12
…..(di +)

6y + 3z = 0 –> 2y + z = 0
z = – 2y …(1)

3x + 5y + 4z = 6 ….(kali 1)
x  + y – 2z = 6………(kali 3)
…
3x + 5y + 4z = 6
3x + 3y -6z = 18
…di(-)
2y + 10z = – 12   dan z = -2y
2y + 10(-2y) = -12
-18 y = -12
y = 2/3  dan z  = – 2y = – 4/3

2x + 4y – z = 12
2x +4(2/3) – (-4/3) = 12
2x + 8/3 + 4/3 = 12
2x + 4 = 12
x = 4