In order to solve $ \color{blue}{ 5x^{11}+10x^{10}-35x^{9} = 0 } $, first we need to factor our $ x^9 $.
$$ 5x^{11}+10x^{10}-35x^{9} = x^9 \left( 5x^{2}+10x-35 \right) $$$ x = 0 $ is a root of multiplicity $ 9 $.
The remaining roots can be found by solving equation $ 5x^{2}+10x-35 = 0$.
$ 5x^{2}+10x-35 = 0 $ is a quadratic equation.
You can use step-by-step quadratic equation solver to see a detailed explanation on how to solve this equation.