In order to solve $ \color{blue}{ 3x^{4}+x^{3}-14x^{2}-2x = 0 } $, first we need to factor our $ x $.
$$ 3x^{4}+x^{3}-14x^{2}-2x = x \left( 3x^{3}+x^{2}-14x-2 \right) $$$ x = 0 $ is a root of multiplicity $ 1 $.
The remaining roots can be found by solving equation $ 3x^{3}+x^{2}-14x-2 = 0$.
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using qubic formulas.