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: a mixture of 70 litres of milk and water contains 10 % water. how many litres of water should be added to the mixture so that the mixture contains 12 1 / 2 % water ?
Options: a. 2, b. 8, c. 6, d. 3, e. 4
Example Output: a

Example Input: Problem: a boat having a length 8 m and breadth 2 m is floating on a lake. the boat sinks by 1 cm when a man gets on it. the mass of the man is :
Options: a. 12 kg, b. 60 kg, c. 72 kg, d. 160 kg, e. none of these
Example Output: d

Example Input: Problem: a man invested rs. 14,400 in rs. 100 shares of a company at 25 % premium. if the company declares 5 % dividend at the end of the year, then how much does he get ?
Options: a. rs. 576, b. rs. 600, c. rs. 650, d. rs. 720, e. none
Example Output:
a