Please use * to indicate mult., not "x."
Then 2^2*2^n = (2^4)^3
4*2^n = 16^3
2 is the base of the first exponential, and 16 is the base of the second.
Rewrite 16 as 2^4 (as it was originally given).
Then 4*2^n = (2^4)^3
This is equivalent to 2^(n+2) = 2^12
Solving for n: n+2 = 12, and so n = 10 (answer. You should check this.