The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -1.7083\\[1 em]x_2 &= 4.8542+1.011i\\[1 em]x_3 &= 4.8542-1.011i \end{aligned} $$Polynomial $ x^3-8x^2+8x+42 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.