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 man spends 2 / 5 of his salary on house rent, 3 / 10 of his salary on food and 1 / 8 of his salary on convenience he has rs. 1400 left with him, find his expenditure on food and conveyance.
Options: a. 1000, b. 3000, c. 4000, d. 2000, e. 5000
Example Output: a

Example Input: Problem: 3 ltr of water is added with 9 ltr of a solution containing 57 % of alcohol in the water. the % of alcohol in the new mixture is ?
Options: a. 41.5 %, b. 42.75 %, c. 43 %, d. 45 %, e. 45.75 %
Example Output: b

Example Input: Problem: how many seconds will a 500 m long train take to cross a man walking with a speed of 3 km / hr in the direction of the moving train if the speed of the train is 63 km / hr ?
Options: a. 22, b. 30, c. 88, d. 26, e. 12
Example Output:
b