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: two taps a and b can fill a cistern in 12 minutes and 18 minutes respectively. they are turned on at the same time. if the tap a is turned off after 4 minutes, how long will tap b take to fill the rest of the cistern ?
Options: a. 8 min., b. 9 min., c. 10 min., d. 7 min., e. none of these
Example Output: a

Example Input: Problem: to deliver an order on time, a company has to make 25 parts a day. after making 25 parts per day for 3 days, the company started to produce 5 more parts per day, and by the last day of work 100 more parts than planned were produced. find how many parts the company made and how many days this took.
Options: a. 600, b. 500, c. 575, d. 655, e. 675
Example Output: e

Example Input: Problem: an article with cost price of 240 is sold at 20 % profit. what is the selling price ?
Options: a. 288, b. 200, c. 204, d. 207, e. 210
Example Output:
a