The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 4.6864\\[1 em]x_2 &= -2.3432+1.8632i\\[1 em]x_3 &= -2.3432-1.8632i \end{aligned} $$Polynomial $ x^3-13x-42 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.