Question

3x - y = 6 and y = x - 4, use addition to solve the linear system of equations.

Answer 1

3x-y=6
y=x-4
solve by substitution
3x-x+4=6
2x=2
x=1

Now that you know x, but in in the equation to find y (either equation will work)
y= 1-4
y= -3

now that you have both answers, let's check them.

3(-1) - (-3) =6
yes, it works....

Hopefully this makes sense!