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: if a mixture is 1 ⁄ 7 alcohol by volume and 2 ⁄ 7 water by volume, what is the ratio of the volume of alcohol to the volume of water in this mixture ?
Options: a. 4 / 2, b. 3 / 2, c. 1 / 2, d. 5 / 2, e. 7 / 2
Example Output: c

Example Input: Problem: last year elaine spent 20 % of her annual earnings on rent. this year she earned 35 % more than last year and she spent 30 % of her annual earnings on rent. the amount she spent on rent this year is what percent of the amount spent on rent last year ?
Options: a. 202.5, b. 194.5, c. 197.5, d. 182.5, e. 177.5
Example Output: a

Example Input: Problem: a, b and c start a business each investing 20,000. after 6 months a withdrew 5000, b withdrew 4000 and c invests 6000 more. at the end of the year, a total profit of 67,600 was recorded. find the share of b.
Options: a. 20,000, b. 21,200, c. 21,600, d. 20,500, e. none of these
Example Output:
c