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: heinz produces tomato puree by boiling tomato juice. the tomato puree has only 20 % water while the tomato juice has 90 % water. how many liters of tomato puree will be obtained from 25 litres of tomato juice ?
Options: a. 2.8 liters., b. 3.125 liters., c. 8.5 liters., d. 2.6 liters., e. 2.1 liters.

Ex Output:
b


Ex Input:
Problem: set s consists of integers { 7, 8, 10, 12, 13 }. if integer n is included in the set, the average ( arithmetic mean ) of set s will increase by 10 %. what is the value of integer n ?
Options: a. 10, b. 12, c. 16, d. 22, e. 24

Ex Output:
c


Ex Input:
Problem: the current in a river is 10 mph. a boat can travel 50 mph in still water. how far up the river can the boat travel if the round trip is to take 5 hours ?
Options: a. 120, b. 100, c. 96, d. 85, e. 150

Ex Output:

a