x+2y+2z=3 4x+2y-z=13 2x+y-2z=9

2x + y - 2z = 9
x + 2y + 2z =3
------------------- (+)
3x + 3y = 12

4x + 2y - z = 13  (x2)   -> 8x + 4y - 2z = 26
2x + y - 2z = 9    (x1)   -> 2x + y - 2z = 9
                                        ------------------------ (-)
                                        6x + 3y = 17
                                        3x + 3y = 12
                                        ------------------ (-)
                                        3x = 5
                                          x = 5/3

3(5/3) + 3y = 12
       5 + 3y = 12
               y = 7/3

4(5/3) + 2(7/3) - z = 13
20/3 + 14/3 - z = 13
6/3 - 13 = z
2 - 13 = z
z = -11

maaf jika ada salah :)