An arithmetic progression has third term 90 and fifth term 80.

(i) Find the first term and the common difference.

(ii) Find the value of \(m\) given that the sum of the first \(m\) terms is equal to the sum of the first \((m + 1)\) terms.

(iii) Find the value of \(n\) given that the sum of the first \(n\) terms is zero.