Answer
$\color{blue}{(3-r)(9+3r+r^2)}$
Work Step by Step
With $27=3^3$, the given polynomial is equivalent to:
$=3^3-r^3$
Factor using the formula $x^3-y^3=(x-y)(x^2+xy+y^2)$ with $x=3$ and $y=r$ to obtain:
$=(3-r)(3^2+3\cdot r + r^2)
\\=\color{blue}{(3-r)(9+3r+r^2)}$
