Question

x-z=7
x+y=3
z-y=6
What does x=

Answer 1

What you need to lok at is that you have three different equations here, so you can solve for a term and then plug it into another one to get the answer of another term.

Answer 2

For example:
Start with x-z=7
You can either solve for z or x here, and then whatever you get, plug it into the other equations, and it will give you an actual number