The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -2.1049\\[1 em]x_2 &= 0.5524+1.7379i\\[1 em]x_3 &= 0.5524-1.7379i \end{aligned} $$Polynomial $ x^3+x^2+x+7 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.