The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.0696\\[1 em]x_2 &= 2.9652+4.9864i\\[1 em]x_3 &= 2.9652-4.9864i \end{aligned} $$Polynomial $ x^3-7x^2+40x-36 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.