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1. An arithmetic sequence has a common difference of 2 and a sum of 120. The first term is numerically equal to the number of terms. FInd all possible values of hte first.

I know that the answer is 8 because it is a multiple choice question and through elimination, the others aren't possible, but I don't understand how to prove this mathematically.

2. Determine Sn of the series 4 + 10 + 16 + 22+...+ (6n - 2).

I tried to solve this one, but when I did, the n's cancelled out, making it "all real numbers" and since (6n - 2) is the last term, the series isn't infinite.

PLEASE HELP ME!!! Thanks!