Answer
$531440$
Work Step by Step
First, we must determine the common ratio between the terms:
$r=\frac{6}{2}=\frac{18}{6}=\frac{54}{18}=3$
For solving this, we will use the formula for the $nth$ term of the geometric series. $S_{n}=\frac{a_{1}\times (1-r^{n})}{1-r}$. Then put correct value for $7th$ term to solve.
$S_{12}=\frac{2 \times (1-3^{12})}{1-3}=531440$
