$$-x^3+4x^2+90x-15 = 0$$
Answer
$$ \begin{matrix}x_1 = 0.1655 & x_2 = -7.79411 & x_3 = 11.62861 \end{matrix} $$
Explanation
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using qubic formulas.
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Polynomial Equations Solver