x+y-z=3 (1)
x-y+z=-3 (2)
-x+y+z=6 (3)
(1)+(2)+(3)
x+y+z=6 (4)
(4)-(1)
2z=3
(4)-(2)
2y=9
所以
y=9/2
z=3/2
x=z+3-y=6