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: a person ' s present age is two - fifth of the age of his mother. after 8 years, he will be one - half of the age of his mother. how old is the mother at present
Options: a. 38, b. 40, c. 42, d. 44, e. 45
Example Output: b

Example Input: Problem: a train of length 250 m crosses a bridge of length 150 m in 20 seconds. what is the speed of train ?
Options: a. 33, b. 27, c. 25, d. 22, e. 72
Example Output: e

Example Input: Problem: set s contains exactly 10 numbers and has an average ( arithmetic mean ) of 6.2. if one of the numbers in set s is increased by 7, while all other numbers remain the same, what is the new average of set s ?
Options: a. 6.6, b. 6.7, c. 6.8, d. 6.85, e. 6.9
Example Output:
e