The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2.6803\\[1 em]x_2 &= -2.4834\\[1 em]x_3 &= 33.8031 \end{aligned} $$Polynomial $ -x^3+34x^2-225 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.