Answer
$$-6x\sqrt{x+5}$$
Work Step by Step
In order to simplify the expression, we first simplify each of the terms, and then we combine like terms. Doing this, we find:
$$ \sqrt{20x^2+4x^3}-3x\sqrt{45+9x}+\sqrt{5x^2+x^3}\\ 2x\sqrt{x+5}-9x\sqrt{x+5}+x\sqrt{x+5}\\ -6x\sqrt{x+5}$$
