The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -1.279\\[1 em]x_2 &= 2.1395+0.9463i\\[1 em]x_3 &= 2.1395-0.9463i \end{aligned} $$Polynomial $ x^3-3x^2+7 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.