In order to solve $ \color{blue}{ -12x^{11}+27x^{7} = 0 } $, first we need to factor our $ x^7 $.
$$ -12x^{11}+27x^{7} = x^7 \left( -12x^{4}+27 \right) $$$ x = 0 $ is a root of multiplicity $ 7 $.
The remaining roots can be found by solving equation $ -12x^{4}+27 = 0$.
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using quartic formulas