The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.7021\\[1 em]x_2 &= -1.5177+1.2225i\\[1 em]x_3 &= -1.5177-1.2225i \end{aligned} $$Polynomial $ 3x^3+7x^2+5x-8 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.