The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2.1336\\[1 em]x_2 &= -0.0668+0.6369i\\[1 em]x_3 &= -0.0668-0.6369i \end{aligned} $$Polynomial $ 8x^3-16x^2+x-7 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.