Doubt in rules of exponents

In this problem here, we know that n^2 has to have at least 3 threes and 3 twos. They’re trying to revert back to n, make it 2 twos and 2 threes to find the answer. However, I tried to stick with n^2. I tried to find which number, when squared has at least 3 threes and 3 twos. In this case,

12^2 = (3^2 * 2^4)
24^2 = (2^6 * 3^2)
36^2 = (2^4 * 3^4)
72^2 = (3^4 * 2^6)

And the answers are only 36 and 72 but not 12 and 36 as in the original answer. Why?
Any response that can solve my query is appreciated. Thanks in advance!

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Thank you