The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.8851\\[1 em]x_2 &= -3.753\\[1 em]x_3 &= 5.118 \end{aligned} $$Polynomial $ 4x^3-9x^2-72x+68 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.