Answer
$3r(r+5)(r-14)$
Work Step by Step
$ 3r^{3}-27r^{2}-210r\qquad$...factor out the common term, $3r$
$=3r(r^{2}-9r-70)$
Two factors of $ac=-70$, whose sum is $b=-9$
are $5$ and $-14$.
Rewrite the middle term and factor in pairs.
$3r(r^{2}-9r-70)$
$=3r(r^{2}+5r-14r-70)$
$=3r[r(r+5)-14(r+5)]\qquad$...factor out the common binomial factor,$r+5$.
$=3r(r+5)(r-14)$
