\[4,\ 12,\ 36,\ldots,324,\ldots\]
\[q = \frac{12}{4} = 3;\ \ \ \ a_{n} = 324\]
\[4 \cdot q^{n - 1} = 324\]
\[q^{n - 1} = 81\]
\[3^{n - 1} = 3^{4}\]
\[n - 1 = 4\ \ \]
\[n = 5.\]
\[Ответ:n = 5.\]