x+y-z=11 (1)
y+z-x=5 (2)
z+x-y=1 (3)
(1)+(2)+(3)
x+y+z=17 (4)
(4)-(2)
2x=12
(4)-((3)
2y=16
所以
x=6
y=8
z=x+y-11=3