Answer
See below.
Work Step by Step
The nth term of a geometric series can be obtained by the following formula: $a_n=a_1\cdot r^{n-1}$, where $a_1$ is the first term and $r$ is the common ratio.
Here the common ratio is $5$ and $a_1=3$.
Hence here: $a_6=a_1\cdot2^{6-1}$, thus $a_1=-3$, hence $a_n=-3\cdot(2)^{n-1}$, thus $a_8=-3\cdot(2)^{8-1}=-384$
