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: what is the sum of natural numbers between 30 and 100
Options: a. 4615, b. 4860, c. 5000, d. 5500, e. 5550
Example Output: a

Example Input: Problem: lloyd normally works 7.5 hours per day and earns $ 3.50 per hour. for each hour he works in excess of 7.5 hours on a given day, he is paid 1.5 times his regular rate. if lloyd works 10.5 hours on a given day, how much does he earn for that day ?
Options: a. $ 33.75, b. $ 42.00, c. $ 51.75, d. $ 54.00, e. $ 70.00
Example Output: b

Example Input: Problem: a car averages 65 mph for the first 5 hours of a trip and averages 75 mph for each additional hour. the average speed for the entire trip was 60 mph. how many hours long is the trip ?
Options: a. 9, b. 8, c. 7, d. 6, e. 5
Example Output:
a