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.

Example Input: Problem: the average runs scored by a batsman in 30 matches is 50. in the next 15 matches the batsman scored an average of 26 runs. find his average in all the 45 matches ?
Options: a. 31, b. 42, c. 29, d. 97, e. 27
Example Output: b

Example Input: Problem: dhoni bought 5 toys with the average cost of $ 10. if david also buys the sixth toy with the price of $ 16, what is the average ( arithmetic mean ) price of those 6 toys ?
Options: a. $ 10, b. $ 7, c. $ 8.5, d. $ 9, e. $ 11
Example Output: e

Example Input: Problem: if the cost price of 50 articles is equal to the selling price of 45 articles, then the gain or loss percent is ?
Options: a. 11.11, b. 65, c. 78, d. 33, e. 25
Example Output:
a