One method would be to get the variable terms in each equation onto the left-hand sides, and the constant terms onto the right-hand sides. Simplify. (For instance, the first equation would become "x - y = 7".) Then solve the resulting (simplified) system by whichever method you have been taught.
If you get stuck, please reply showing your steps, and specifying the method (Cramer's Rule? Gauss-Jordan elimination? substitution? etc) that you are using.
You can check yourself. Substitute these values into the original equations and see if they work. If you get something like 3 = 7.2, then it's back to the drawing board. If you get 0 = 0, twice, you're done. No more need to doubt.