Question

Least common denominator y/y+4 + 4/y^2-16

Answer 1

(Y+4)(Y-4)

You need both

Answer 2

First factor the second fraction's denominator.
It is a difference of squares so it can be factored as (y + 4)(y - 4)

Notice the first fraction's denominator is y + 4. So you already have that.
Therefore the LCD is (y + 4)(y - 4) :)