Add 2nd and 3rd equations to eliminate y: 9x-z=3, from which z=9x-3.
Multiply the 1st equation by 6: 18x+6y-36z=102 and add to the 3rd equation:
23x-32z=96. Substitute 9x-3 for z:
23x-32(9x-3)=96,
23x-288x+96=96,
therefore x=0. z=9x-3=0-3=-3.
Substitute x=0 and z=-3 in the first equation:
0+y+18=17, y=-1.
SOLUTION (x,y,z)=(0,-1,-3).