The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -5.1399\\[1 em]x_2 &= -9.93+59.5761i\\[1 em]x_3 &= -9.93-59.5761i \end{aligned} $$Polynomial $ x^3+25x^2+3750x+18750 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.