The sum of the first nine terms of an ap is 72 and the sum of the next four terms is 71.find the ap

Answer 1

Please help me solve this problem

Answer 2

S9 = 72
S13-S9 = 71

9/2 (2a+8d) = 72
13/2 (2a+12d) - 72 = 71

Now solve for a and d as usual.