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: last year elaine spent 20 % of her annual earnings on rent. this year she earned 35 % more than last year and she spent 30 % of her annual earnings on rent. the amount she spent on rent this year is what percent of the amount spent on rent last year ?
Options: a. 202.5, b. 194.5, c. 197.5, d. 182.5, e. 177.5
Example Output: a

Example Input: Problem: if the population of a certain country increases at the rate of one person every 45 seconds, by how many persons does the population increase in 1 hour ?
Options: a. 80, b. 120, c. 150, d. 180, e. 160
Example Output:
a