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 student travels from his house to school at 10 km / hr and reaches school 2 hours late. the next day he travels 18 km / hr and reaches school 1 hour early. what is the distance between his house and the school ?
Options: a. 65.0, b. 67.5, c. 70.0, d. 72.5, e. 75.0
Example Output: b

Example Input: Problem: a and b invests rs. 2500 and rs. 4000 respectively in a business. if a doubles his capital after 6 months. in what ratio should a and b divide that year ' s profit ?
Options: a. 11: 5, b. 15: 16, c. 15: 2, d. 9: 9, e. 11: 1
Example Output: b

Example Input: Problem: a piece of cloth cost rs 35. if the length of the piece would have been 4 m longer and each meter cost re 1 less, the cost would have remained unchanged. how long is the piece ?
Options: a. 5 mtrs, b. 10 mtrs, c. 12 mtrs, d. 15 mtrs, e. 18 mtrs
Example Output:
b