Answer
The sequence is geometric.
$a_{n}=3\cdot 4^{n-1}$
Work Step by Step
$\dfrac{12}{3}=\dfrac{48}{12}=\dfrac{192}{48}=\dfrac{768}{192}=\dfrac{3072}{768}=4$
As $\frac{a_{n+1}}{a_{n}}=4$, that is, the ratio between each term and the preceding term is the same, the sequence is geometric.
Common ratio: $r=4$.
First term: $a_{1}=3$.
The general term is:
$a_{n}=a_{1}\cdot r^{n-1}=3\cdot 4^{n-1}$
