just plug in your formulas. If you mean
"the sum of the first 8 terms" then
8/2 (2a + 7d) = 549
You have d, so find a, and then
a + 55d
and
32/2 (2a + 31d)
the sum of 8th terms of an AP is 549 while the common difference is 3. find the 56th term and the sum of it's 32 terms
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