Answer
$(x +3)(x^2 -3x +9)$
Work Step by Step
Since $x^3+27$ is a sum of the two cubes $x^3$ and $3^3$, then by making use of the sum of two cubes
$$a^3 + b^3 = (a + b)(a^2 - ab + b^2),$$
we have
\begin{align*}
x^3 +27&=x^3+3^3\\
&= (x +3)(x^2 -3x + 3^2)\\
&= (x +3)(x^2 -3x +9)
\end{align*}
