How do I find the first four terms for an arithmetic sequence

The two formulas you need to know:

Find any term in an arithmetic sequence: An = A1 + (n-1) d

where A1 = is the first term, n is the number in the sequence, and d is the common difference.

Find the sum of an arithmetic sequence: Sn = 0.5n (A1+An).

To solve d, we need to know n for the An=67. To do this we can use the sum equation:

Sn = 0.5n (A1+An)

680 = 0.5n (10+67)

n = (2*680) / (10+67) = 17.66