.
Since the post by @josgrithmetic contains ERRORS,
I came to bring a correct solution.
0.4x^2 - 5x + 4.9 = 5x
0.4x^3 - 10x + 4.9 = 0
0.1*(4x^2 - 100x + 49) = 0
0.1*(2x-49)*(2x-1) = 0.
Done.
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He changed/corrected his post after seeing my post.