Answer
r($r^{2}$ + 18r + 108)
Work Step by Step
$(r + 6)^{3}$ - 216 is a difference of cubes, so we write it as a diference of cubes and factor:
$(r + 6)^{3}$ - $6^{3}$
= (r + 6 - 6)($(r + 6)^{2}$ + (r + 6)(6) + $6^{2}$)
= r($r^{2}$ + 12r + 36 + 6r + 36 + 36)
= r($r^{2}$ + 18r + 108)
