x+y=22 (1)
y+z=13 (2)
z+x=-27 (3)
(1)+(2)+(3)
2(x+y+z)=8
x+y+z=4 (4)
(4)-(2)
x=-9
(4)-(3)
y=31
(4)-(1)
z=-18
x=-9 y=31 z=-18