Assuming that these two equations aren't being multiplied:
solve the second equation for y
5y+9z=1 5y=1-9z y=(1-9z)/5
substitute y for 0
0=(1-9z)/5
5=1-9z
We could leave it like this, but I'm not going to because it feels so unfinished.
5-1=-9z
4=-9z
-4/9=z
x+z=6
x-(4/9)=6
x=6+(4/9)
x=58/9
