Um wow, I can't really tell you all of this but I got my answers from "cymath.com" So here is what it says:)
"Solve for xx in 2x+2z=42x+2z=4How?
x=2-zx=2−z
2 Substitute x=2-zx=2−z into -x-y-z=-8−x−y−z=−8How?
-y-2=-8−y−2=−8
3 Substitute x=2-zx=2−z into -4x+4y+5z=7−4x+4y+5z=7How?
-8+9z+4y=7−8+9z+4y=7
4 Solve for yy in -y-2=-8−y−2=−8How?
y=6y=6
5 Substitute y=6y=6 into -8+9z+4y=7−8+9z+4y=7How?
9z+16=79z+16=7
6 Substitute y=6y=6 into x=2-zx=2−zHow?
x=2-zx=2−z
7 Solve for zz in 9z+16=79z+16=7How?
z=-1z=−1
8 Substitute z=-1z=−1 into x=2-zx=2−zHow?
x=3x=3
9 Therefore,
x=3x=3
y=6y=6
z=-1z=−1"
