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: car z travels 50 miles per gallon of gasoline when driven at a constant rate of 45 miles per hour, but travels 20 percent fewer miles per gallon of gasoline when driven at a constant rate of 60 miles per hour. how many miles does car z travel on 10 gallons of gasoline when driven at a constant rate of 60 miles per hour ?
Options: a. 320, b. 375.2, c. 400, d. 408.3, e. 440
Example Output: c

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: 12 spheres of the same size are made from melting a solid cylinder of 8 cm diameter and 27 cm height. what is the diameter of each sphere ?
Options: a. 2 cm, b. 4 cm, c. 6 cm, d. 8 cm, e. 10 cm
Example Output:
c