3x+y+2z=1
x+2y-z=-8
3x-y-3z=18
after I isolate x what is the 2nd equation
depends on how you isolate x.
isolate it from the first equation and you have 1/3 * (1-y-2z) + 2y -z = 8
1-y-2z + 6y -3z = 24
5y -5z = 23
Anyway, you end up with (x,y,z) = (15, -6, 11)