Answer
See below.
Work Step by Step
The ratio of subsequent terms is constant, hence it is a geometric sequence with $a_1=3$ and common ratio $5$. Thus the next term is $5\cdot375=1875$.
The nth term of an arithmetic sequence can be obtained by the following formula: $a_n=a_1+(n-1)d$, where $a_1$ is the first term and $d$ is the common difference.
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.
Hence here $a_n=3(5)^{n-1}$
