2x+3y-z=9(1)
x+y+z=15(2)
5x-4y-z=0(3)
(1)+(2) 3x+4y=24(4)
(2)+(3) 6x-3y=15(5)
(4)*2 6x+8y=48(6)
(6)-(5) 11y=33
y=3
3x=24-4y=24-12=12
x=4
z=15-x-y=15-4-3=8
x=4,y=3,z=8