The first, third and fourth terms of a sequence are given as 2y−1, y+1 and 4y−2 respectively.
a. (i) Show that the sequence can be an arithmetic progression only for specific value(s) of y and find that value.
b. (ii) Using the value of y obtained, write the first five terms of the progression.
c. (iii) Find the sum of the first 25 terms.