The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -8.9399\\[1 em]x_2 &= 0.9699+0.6337i\\[1 em]x_3 &= 0.9699-0.6337i \end{aligned} $$Polynomial $ x^3+7x^2-16x+12 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.