The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.4162\\[1 em]x_2 &= -2.1239\\[1 em]x_3 &= 14.7077 \end{aligned} $$Polynomial $ -x^3+13x^2+26x-13 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.