The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -1.7392\\[1 em]x_2 &= 0.8696+1.8079i\\[1 em]x_3 &= 0.8696-1.8079i \end{aligned} $$Polynomial $ x^3+x+7 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.