The roots of polynomial $ p(r) $ are:
$$ \begin{aligned}r_1 &= 0.5874\\[1 em]r_2 &= -1.7937+1.3747i\\[1 em]r_3 &= -1.7937-1.3747i \end{aligned} $$Polynomial $ r^3+3r^2+3r-3 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.