Answer:
You stopped at 2y-4=12
If we add same number to both sides the equation will remain true. For example if we have 5=5, and we add 7 to both sides, we get 12=12 which is also true. Now let's do this with our equation. Add 4 to both sides(to have only y on the left side). We get 2y=16, hence y=8.
Answer. 2y=16