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: last year elaine spent 20 % of her annual earnings on rent. this year she earned 20 % 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. 185.5, b. 180.0, c. 167.5, d. 172.5, e. 177.5
Example Output: b

Example Input: Problem: the sum of the ages of 5 children born at the intervals of 3 year each is 60 year. what is the age of the youngest child ?
Options: a. 4 year, b. 6 year, c. 10 year, d. none of these, e. 9 year
Example Output: b

Example Input: Problem: a person borrows 20000 for 6 years at 8 % p. a. simple interest. he immediately lends it to another person at 9 % p. a. for 6 years. find his gain in the transaction per year.
Options: a. 200, b. 250, c. 210, d. 190, e. 180
Example Output:
a