Answer
$2049$
Work Step by Step
First, we must determine the common ratio between the terms:
$r=\frac{-6}{3}=\frac{12}{-6}=\frac{-24}{12}=-2$
For solving this, we will use the formula of the finite geometric series. $S_{n}=\frac{a_{1}\times (1-r^{n})}{1-r}$. Then put correct value for $7th$ term to solve.
$S_{11}=\frac{3 \times (1-(-2)^{11})}{1-(-2)}=2049$
