Answer
$$ x^4+4x^3-3x^2-18x$$
Work Step by Step
Expanding the equations by multiplying each term in parenthesis by each of the other terms in the other set of parenthesis, we find:
$$\left(x\right)x\left(x+3\right)^2-2\left(x\right)\left(x+3\right)^2\\ x^4+4x^3-3x^2-18x$$
