There are like terms 5y and y. Since there is a subtraction sign in front of y, we would subtract that from 5y, which becomes 4y. 8x and 12x are also like terms (x). Since 12x has an addition sign in front, indicating it's positive, we would add it to -8x (which is negative b/c of the subtraction sign in front). 12x + -8x = 4x. The expression is 4y + 4x.
Hope this helps!
