Instructions: 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.
Input: Problem: a cistern has a leak which would empty the cistern in 20 minutes. a tap is turned on which admits 4 liters a minute into the cistern, and it is emptied in 24 minutes. how many liters does the cistern hold ? a. 480 liters
Options: a. 480, b. 489, c. 486, d. 482, e. 483
Output:
a