The 14th term of an arithmetic progression is 96 while the 25th term is 173 find the sum of the 13th term and the 56th
a+13d = 96
a+24d = 173
solve for a and d, and then you want
a+12d + a+55d = 2a+67d
a+24d = 173
solve for a and d, and then you want
a+12d + a+55d = 2a+67d