The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 6.7937\\[1 em]x_2 &= 0.1032+3.2538i\\[1 em]x_3 &= 0.1032-3.2538i \end{aligned} $$Polynomial $ -x^3+7x^2-12x+72 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.