The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.1939\\[1 em]x_2 &= -0.9032\\[1 em]x_3 &= 3.7093 \end{aligned} $$Polynomial $ x^3-4x^2+4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.