I'm thinking to solve it a different way...
We have:
\(81^n=9^{27} \cdot 27^9\)
We know 81 is 3^4
\((3^4)^n = 9^{27} \cdot 27^9\)
So the left side simplifies to
\(3^{4n} = 9^{27} \cdot 27^9\)
We know 9 is 3^2 and 27 is 3^3 so we use that information into our equation:
\(3^{4n} = (3^2)^{27} \cdot (3^3)^9\)
So the right side simplifies to:
\(3^{4n} = (3^{54}) \cdot (3^{27})\)
Then, we know that if we have the same base when multiplying, we add the exponents so:
\(3^{4n} = (3^{81})\)
So:
\(4n = 81 \)
Divide by 4 to both sides:
\(n = 81/4 = 20.25\)
This is (I believe) the standard and faster way to solve it in a real competition.