The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 8.6975\\[1 em]x_2 &= -0.0154+0.5177i\\[1 em]x_3 &= -0.0154-0.5177i \end{aligned} $$Polynomial $ 3x^3-26x^2-7 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.