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.

Ex Input:
Problem: a bag has 9 green balls and 23 pink balls. how many green balls should be added to the bag so that the ratio of green balls and pink balls in the bag becomes 1: 1 ?
Options: a. 10, b. 11, c. 12, d. 13, e. 14

Ex Output:
e


Ex Input:
Problem: a man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. the ratio of the speed of the boat in still water and stream is
Options: a. 3: 1, b. 1: 3, c. 2: 4, d. 4: 2, e. none of these

Ex Output:
a


Ex Input:
Problem: two pipes a and b can separately fill a tank in 12 and 15 minutes respectively. a third pipe c can drain off 45 liters of water per minute. if all the pipes are opened, the tank can be filled in 15 minutes. what is the capacity of the tank ?
Options: a. 399, b. 540, c. 772, d. 272, e. 121

Ex Output:

b