x+y-z=-4.5 (1)
x-2y+3z=3 (2)
3x+2y-z=-7 (3)
(1)×2+(2)
3x+z=-6 (4)
(2)+(3)
4x+2z=-4
2x+z=-2 (5)
(4)-(5)
所以
x=-4
z=-2-2x=6
y=-4.5+z-x=5.5