I am 7.

Let n represent the number.

Add 47 to me.
47 + n

Multiply the sum by 3.
(47 + n)3

Divide the product by 2.
((47 + n)3) / 2

You end up with 81.
((47 + n)3) / 2 = 81
(47 + n)3 = 162
47 + n = 54
n = 7

 

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