Answer
$3\left( x+3\right) \left( 9x^{2}+25x+21\right) $
Work Step by Step
$\left( 3x+4\right) ^{3}-1=\left( 3x+4\right) ^{3}-1^{3}=\left( 3x+4-1\right) \left( \left( 3x+4\right) ^{2}+1\times \left( 3x+4\right) +1^{2}\right) =3\left( x+3\right) \left( 9x^{2}+25x+21\right) $
