Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

[EX Q]: Problem: the average runs scored by a batsman in 20 matches is 40. in the next 10 matches the batsman scored an average of 30 runs. find his average in all the 30 matches ?
Options: a. 31, b. 36.67, c. 88, d. 13, e. 12
[EX A]: b

[EX Q]: Problem: a man can row upstream at 25 kmph and downstream at 55 kmph, and then find the speed of the man in still water ?
Options: a. 65, b. 40, c. 30, d. 78, e. 38
[EX A]: b

[EX Q]: Problem: in a family 13 people eat only vegetarian, 8 people eat only non veg., 6 people eat both veg and non veg.. how many people eat veg in the family ?
Options: a. 20, b. 11, c. 19, d. 31, e. 21
[EX A]:
c