The third term is 8, the 8th term is 23. So, in the space of 5 terms, we covered a "distance" of 15. Thus, the common difference is 15/5 or 3.

To find the first term, let's work backwards from the third term. Since we're working backwards, instead of adding 3, we'll subtract 3.

Second term = 8 - 3 = 5.

Third term = 5 - 3 = 2.