For an arithmetic progression whose first term is a and common difference is d, the sum of the terms from the (n+1)th term to the (2n)th term equals 5 times the first term and is also equal to 180.
a. (i) Obtain an expression, in terms of a, d and n, for the sum of the terms from the (n+1)th term to the (2n)th term.
b. (ii) Hence form two equations involving a, d and n.
c. (iii) If the common difference d is a positive integer less than 10, determine the values of a, d and n.