In order to solve $ \color{blue}{ -16x^{20}-72x^{17}-81x^{14} = 0 } $, first we need to factor our $ x^14 $.
$$ -16x^{20}-72x^{17}-81x^{14} = x^14 \left( -16x^{6}-72x^{3}-81 \right) $$$ x = 0 $ is a root of multiplicity $ 14 $.
The remaining roots can be found by solving equation $ -16x^{6}-72x^{3}-81 = 0$.
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using Newton method.