The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -6.0309\\[1 em]x_2 &= -0.4845+1.3859i\\[1 em]x_3 &= -0.4845-1.3859i \end{aligned} $$Polynomial $ x^3+7x^2+8x+13 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.