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 hiker walking at a constant rate of 4 kilometers per hour is passed by a cyclist travelling in the same direction along the same path at a constant rate of 24 kilometers per hour. the cyclist stops and waits for the hiker 5 minutes after passing her while the hiker continues to walk at her constant rate. how many minutes must the cyclist wait until the hiker catches up ?
Options: a. 10, b. 15, c. 20, d. 25, e. 30
Example Output: d

Example Input: Problem: a student took 5 papers in an examination, where the full marks were the same for each paper. his marks in these papers were in the proportion of 6: 7: 8: 9: 10. in all papers together, the candidate obtained 60 % of the total marks then, the number of papers in which he got more than 50 % marks is
Options: a. 1, b. 3, c. 4, d. 5, e. 7
Example Output: c

Example Input: Problem: how many of the integers between 15 and 55 are even ?
Options: a. 21, b. 20, c. 11, d. 10, e. 9
Example Output:
b