Answer
$12285$
Work Step by Step
Formula to calculate the sum of the first $n$ terms of a geometric sequence is: $s_n=\dfrac{a(1-r^n)}{(1-r)}$
Here, $r=\dfrac{a_2}{a_1}=2$
As we are given that, $n=12$
Thus, $s_{12}=\dfrac{3(1-2^{12})}{(1-2)}$
or, $s_{12}=12285$
