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: excluding stoppages, the average speed of a bus is 60 km / hr and including stoppages, the average speed of the bus is 40 km / hr. for how many minutes does the bus stop per hour ?
Options: a. 18 min, b. 17 min, c. 19 min, d. 20 min, e. 21 min
Example Output: d

Example Input: Problem: 50 % of a number is more than 40 % of 120 by 180. find the number ?
Options: a. 456, b. 480, c. 420, d. 445, e. 320
Example Output: a

Example Input: Problem: the percentage profit earned by selling an article for rs. 1320 is equal to the percentage loss incurred by selling the same article for rs. 1280. at what price should the article be sold to make 25 % profit ?
Options: a. 3000, b. 1230, c. 2000, d. 1625, e. 3400
Example Output:
d