Hi,
I. 6x-y+2z=-14
II. x+2y-z=-2
III. 2x+2y-3z=-11
I. 12x-2y+4z=-28 |Multiplying EQ I by 2 & adding I an II to eliminate y
II. x+2y-z=-2
A
II. -x-2y+z=2 |Multiplying EQ II by -1 & adding II an III to eliminate y
III. 2x+2y-3z=-11
B
|Multiplying EQ B by -13
29z = 87
z = 3 and x = -3 and y = 2
2x+2y-3z=-11
-6 + 4 - 9 = -11