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: income and expenditure of a person are in the ratio 7: 6. if the income of the person is rs. 14000, then find his savings ?
Options: a. 500, b. 1000, c. 1500, d. 2000, e. 2500
Example Output: d

Example Input: Problem: john can complete a given task in 18 days. jane will take only 12 days to complete the same task. john and jane set out to complete the task by beginning to work together. however, jane was indisposed 6 days before the work got over. in how many days did the work get over from the time john and jane started to work on it together ?
Options: a. 11, b. 34 / 5, c. 44 / 5, d. 54 / 5, e. 12
Example Output: d

Example Input: Problem: if a drawing has an outer circle of diameter 30 and an inner circle of diameter 24, then what fraction of outer circle ' s surface is not covered by the inner circle ?
Options: ['a. 3 / 6', 'b. 8 / 24', 'c. 14 / 16', 'd. 9 / 25', 'e. 2 / 3']
Example Output:
d