For a certain arithmetic progression, the sum of the first n terms is 300 and the sum of the next (n – 3) terms is 312.
(i) Show that n satisfies the quadratic equation n2−7n+6=0 and hence find the value of n.
(ii) Using the value of n obtained in part (i), determine the first term and the common difference.
(iii) Find the 20th term of the progression.