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: a is twice as good a work man as b and together they finish the work in 4 days. in how many days a alone can finish the work ?
Options: a. 3, b. 2, c. 7, d. 9, e. 6
Example Output: e

Example Input: Problem: in traveling from a dormitory to a certain city, a student went 1 / 3 of the way by foot, 3 / 5 of the way by bus, and the remaining 2 kilometers by car. what is the distance, in kilometers, from the dormitory to the city ?
Options: a. 30, b. 45, c. 60, d. 90, e. 120
Example Output: a

Example Input: Problem: 4 balls of different colors are to be placed in 3 different boxes such that any box contains at least 1 ball. what is the maximum number of different ways in which this can be done ?
Options: a. 60, b. 90, c. 120, d. 150, e. 180
Example Output:
e