Instructions: 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.
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
Output:
a