Answer:
the common difference is 5.4 and yes, this is an arithmetic sequence
Explanation:
Each new term is derived by adding 5.4 to the previous term:
2.1 + 5.4 = 7.5,
7.5 + 5.4 = 12.9,
and so on,
so the common difference is 5.4 and yes, this is an arithmetic sequence.