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: the ratio of the present age of viju to that of aju is 7: 2. 4 years from now, the ratio of the ages of viju to aju will be 5: 2. what was viju age 5 years ago ? ( rbi assistant 2015 )
Options: a. 24, b. 18, c. 12, d. 16, e. 13
Example Output: d

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: the owner of a furniture shop charges his customer 20 % more than the cost price. if a customer paid rs. 8600 for a computer table, then what was the cost price of the computer table ?
Options: a. rs. 6289, b. rs. 6298, c. rs. 6290, d. rs. 7166, e. rs. 7708
Example Output:
d