In order to solve $ \color{blue}{ 3x^{5}+2x^{4}-6x^{3}+8x = 0 } $, first we need to factor our $ x $.
$$ 3x^{5}+2x^{4}-6x^{3}+8x = x \left( 3x^{4}+2x^{3}-6x^{2}+8 \right) $$$ x = 0 $ is a root of multiplicity $ 1 $.
The remaining roots can be found by solving equation $ 3x^{4}+2x^{3}-6x^{2}+8 = 0$.
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using quartic formulas