In order to solve $ \color{blue}{ 16x^{4}+8x^{2}-9x = 0 } $, first we need to factor our $ x $.
$$ 16x^{4}+8x^{2}-9x = x \left( 16x^{3}+8x-9 \right) $$$ x = 0 $ is a root of multiplicity $ 1 $.
The remaining roots can be found by solving equation $ 16x^{3}+8x-9 = 0$.
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using qubic formulas.