In order to solve $ \color{blue}{ 6x^{5}-15x^{3}-9x = 0 } $, first we need to factor our $ x $.
$$ 6x^{5}-15x^{3}-9x = x \left( 6x^{4}-15x^{2}-9 \right) $$$ x = 0 $ is a root of multiplicity $ 1 $.
The remaining roots can be found by solving equation $ 6x^{4}-15x^{2}-9 = 0$.
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using quartic formulas