My name is Kelley, I am currently a High School sophomore.
(8 + 5)5 = (y + 4)4
I think that it helps to look at an equation as a balance. You have some weights on one side, (8 + 5)5, balanced with some weights on the other side, (y + 4)4. The object is to move the weights around, without disturbing the balance, to get a situation with y alone on one side and a single number on the other.
With this equation I would first expand both sides.
To isolate the y by itself on one side of the equation you need to eliminate 16 from the right side. You can do this, without disturbing the balance, by subtracting 16 from both sides. That is