The sum of (p + q) th and (p $$-$$ q)th terms of an AP is equal to

What is the fourth term of an AP of n terms whos sum is n(n + 1)?

The sum of the first k terms of a series S is $3k{}^2+5k$. Which one of the following is correct?

The sum of the first 8 terms of a GP is five times the sum of its first 4 terms. If $r$≠$1$ is the common ratio, then what is the number of possible real values of r?