The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -1.2047\\[1 em]x_2 &= 4.1023+3.6131i\\[1 em]x_3 &= 4.1023-3.6131i \end{aligned} $$Polynomial $ x^3-7x^2+20x+36 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.