$$7x^4-420x^3+6600x^2-50000x+750000 = 0$$
Answer
$$ \begin{matrix}x_1 = 22.16846 & x_2 = 38.3963 & x_3 = -0.28238+11.21583i \\[1 em] x_4 = -0.28238-11.21583i & \\[1 em] \end{matrix} $$
Explanation
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using quartic formulas
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