Step 1: Formula for the general term of a GP.
The general term for a geometric progression is given by:
\[
a_n = a_1 r^{n-1}
\]
By comparing the given formula \( a_n = 3(2^n) \) with the general term formula, we can determine that the common ratio \( r = 2 \).
Step 2: Conclusion.
Thus, the common ratio is 2.
Final Answer:
\[
\boxed{2}
\]