x+y-z=11 (1)
y+z-x=3 (2)
z+x-y=1 (3)
(1)+(2)+(3)
x+y+z=15 (4)
(4)-)2)
2x=12
x=6
(4)-(3)
2y=14
所以
x=6
y=7
z=x+y-11=2