$$t^3-9t^2+225 = 0$$
Answer
$$ \begin{matrix}t_1 = -4.1383 & t_2 = 6.56915+3.3491i & t_3 = 6.56915-3.3491i \end{matrix} $$
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