Answer
$a_8=768$
Work Step by Step
RECALL:
The $n^{th}$ term ($a_n$) of a geometric sequence can be found using the formula:
$a_n= a_1 \cdot r^{n-1}$
where
$a_1$ = first term
r = common ratio
Use the formula above and the give values of the first term and the common ratio to obtain:
$a_n=6 \cdot 2^{n-1}
\\a_8=6 \cdot 2^{8-1}
\\a_8=6 \cdot 2^7
\\a_8=6 \cdot 128
\\a_8=768$