3log2(x)-(log2(3)-log2(x+4))
$$\\3log_2(x)-[log_2(3)-log_2(x+4)]\\\\ =3log_2(x)-log_2(3)+log_2(x+4)\\\\ =log_2(x^3)-log_2(3)+log_2(x+4)\\\\ =log_2\;\frac{x^3(x+4)}{3}\\\\$$
I am not sure if that is what you wanted :/