The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.5817\\[1 em]x_2 &= -0.109+0.577i\\[1 em]x_3 &= -0.109-0.577i \end{aligned} $$Polynomial $ 11x^3-15x^2-6 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.