The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 4.2578\\[1 em]x_2 &= -2.6289+2.5448i\\[1 em]x_3 &= -2.6289-2.5448i \end{aligned} $$Polynomial $ x^3+x^2-9x-57 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.