The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.1643\\[1 em]x_2 &= -1.7729\\[1 em]x_3 &= -3.3914 \end{aligned} $$Polynomial $ x^3+4x^2-7 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.