The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.8868\\[1 em]x_2 &= -3.1879\\[1 em]x_3 &= 7.0747 \end{aligned} $$Polynomial $ x^3-3x^2-26x-20 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.