if it’s an arithmetic sequence, the terms are gonna change by a common value (meaning that the difference between consecutive terms is the same). in this case, in order to get from 2 to 8, you add 6, so the third term would be 8+6 which is 14, and the fourth term would be 14+6 which is 20.
so the arithmetic sequence would look like this:
2, 8, 14, 20
hope this helps