x+y=3k (1)
y+z=5k (2)
z+x=4k (3)
(1)+(2)+(3)
2(x+y+z)=12k
x+y+z=6k (4)
(4)-(1)
z=3k
(4)-(2)
x=k
(4)-(3)
y=2k
x-2y+3z=-6
k -4k+9k=-6
6k=-6
k=-1
x+y=3k (1)
y+z=5k (2)
z+x=4k (3)
(1)+(2)+(3)
2(x+y+z)=12k
x+y+z=6k (4)
(4)-(1)
z=3k
(4)-(2)
x=k
(4)-(3)
y=2k
x-2y+3z=-6
k -4k+9k=-6
6k=-6
k=-1