x+y=2k (1)
y+z=3k (2)
z-2x=4k (3)
(1)-(2)
x-z=-k (4)
(3)+(4)
-x=3k
x=-3k
y=2k-x=5k
z=3k-y=-2k
所以-3k+10k+2k=9
k=1