3x-y+z=3 (1)
2x+y-3z=11 (2)
x+y+z=12 (3)
(1)+(2)得到5x-2z=14 (4)
(2)- (3)得到x-4z=-1 (5)
2(4)-(5)得到9x=29 x=29/9
所以y=139/18
z=19/18