The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 15.5596\\[1 em]x_2 &= -0.2798+0.7929i\\[1 em]x_3 &= -0.2798-0.7929i \end{aligned} $$Polynomial $ x^3-15x^2-8x-11 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.