The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.3112\\[1 em]x_2 &= -0.2181+0.7242i\\[1 em]x_3 &= -0.2181-0.7242i \end{aligned} $$Polynomial $ 8x^3-7x^2-6 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.