Hey there!!
We have:
... 3²· 3ⁿ = 3²⁰
Remember the exponent rule:
When the bases are equal and the terms are multiplied, then we add up the exponent.
mⁿ · mˣ = mˣ⁺ⁿ
Hence, this equation would result as :
... 3²⁺ⁿ = 3²⁰
... 2+n=20
... n=18
Hence, the required answer is 18.