The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.572\\[1 em]x_2 &= -1.0861\\[1 em]x_3 &= 3.5141 \end{aligned} $$Polynomial $ x^3-4x^2+6 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.