Explanation:

Let the average be x and so

according to question,

Average = Total no of runs / no of
innings

x = Total no of runs / 12

12x = Total no of runs ----(1)

Also,

In the 13th inning

x + 5 = Total no of runs +96 / 13

13x + 65 = Total no of runs + 96

13x - 31 = Total no of runs ------(2)

Equalling (1) and (2)

12x = 13x - 31

x = 31

Average after 13th inning = 31+5 = 36

Hence, option 3 is the correct answer.