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

the correct answer is 5 6 and 7