Y=2x-20
y=-x+34 it is a substitution method

I will help you do it the correct way.

To solve by substitution, you must cancel out either x or y.
We will choose x, as -x and 2x are easier to change and cancel.
We multiply the second equation by 2 to make -x -2x, the opposite of 2x in the first equation.

y=-x+34
2(y = -x + 34)
2y = -2x + 78

We add the equations together.

y = = 2x - 20
2y = -2x + 68

y + 2y = 2x - 2x + 68 - 20
Combine like terms
3y = 48

isolate y

3y = 48
/3    /3
y = 16

Now we substitute 16 in for y in an original equation.
Let's choose the first equation.

Y=2x-20
16 = 2x - 20
Isolate x

16 = 2x - 20
+20        +20

36 = 2x
/2    /2
18 = x

x = 18
y = 16

The solution is (18, 16)

To check, substitute both into both equations and see whether or not the equation is true. (you can surely do this on your own)