Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10

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First Second Third Forth Fifth Sixth Seventh, Eighth Nine Ten Eleven Twelve.

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How will you do it?

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Who am I?