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: $a_4/a_2=r^2$, thus $r=0.5$, $a_2=a_1\cdot0.5^{2-1}$, thus $a_1=-12$, hence $a_n=-12\cdot(0.5)^{n-1}$, thus $a_8=-12\cdot(0.5)^{8-1}=-0.09375$
