Call the equations in order A, B and C.
A+C: D: 4x+5z=-17;
2B-3C: 4x+6y-2z-(9x+6y+9z)=0-(-45); -5x-11z=45 or E: 5x+11z=-45.
4E-5D: 44z-25z=-180+85; 19z=-95, z=-5. Therefore 4x=-17+25=8, so x=2.
Use any equation to find y by substituting for x and z: 2y=x+2z+2=2-10+2=-6, so y=-3.
Now check out these values in all original equations:
2+6-10=-2; 4-9+5=0; 6-6-15=-15. All check out so the solution is (2,-3,-5) for (x,y,z).
