Answer:
Solution = ( 0, 4 )
Explanation:
You made one tiny error. When you were attempting to substitute your y value, 4, to derive the x - value, you took the second equation. However, that second equation was x + 2y = 8, when you substituted y as 4 you rewrote this equation as x + 2( 4 ) = 12, instead it should have been x + 2( 4 ) = 8!
If you would like, let me explain how to get the right answer;

And as for your " check " let us substitute these values into both the equations, for true confirmation;
