Systems of Equations with Substitution Method

I have a test tomorrow and I can't figure out why I'm ending up with ridiculous numbers when doing this problem...

y + 3x = 7

2x + 3y = 14

Now I know that you're supposed to work with a variable with a coefficient of 1 because it helps you avoid fractions, so I figure it's best to solve for the "y" in "y + 3x = 7".

Here's what I'm doing...I'm trying to get the "y" by itself:

y + 3x = 7

-3x -3x

Is this right^? would it be y= 7 - 3x?

This is only the first step so I might need more help on this.