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: two pipes a and b can fill a tank in 36 hours and 46 hours respectively. if both the pipes are opened simultaneously, how much time will be taken to fill the tank ?
Options: a. 20.195 hrs, b. 21.195 hrs, c. 22.195 hrs, d. 23.195 hrs, e. 20.495 hrs
Example Output: a

Example Input: Problem: an equal number of desks and bookcases are to be placed along a library wall that is 15 meters long. each desk is 2 meters long, and each bookshelf is 1.5 meters long. if the maximum possible number of desks and bookcases are to be placed along the wall, then the space along the wall that is left over will be how many meters f long ?
Options: a. 0.5, b. 1, c. 1.5, d. 2, e. 3
Example Output:
b