The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.7568\\[1 em]x_2 &= 4.7763\\[1 em]x_3 &= -5.5331 \end{aligned} $$Polynomial $ x^3-27x+20 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.