2x-2y+z=-9 (1)
3x+2y-2z=23 (2)
x+y+z=12 (3)
(1)×2+(2)
7x-2y=5 (4)
(1)-(2)
x-3y=-21 (5)
(4)×3-(5)×2
21x-2x=15+42
19x=57
所以
x=3
y=)x+21)/3=8
z=12-x-y=1