The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 3.8589\\[1 em]x_2 &= 1.0706+2.3647i\\[1 em]x_3 &= 1.0706-2.3647i \end{aligned} $$Polynomial $ -x^3+6x^2-15x+26 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.