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 smallest number by which 2880 must be divided in order to make it into a perfect square ?
Options: a. 3, b. 4, c. 5, d. 6, e. 7
Example Output: c

Example Input: Problem: a car is 15 minutes late by running at a speed of 4 / 5 th of its actual speed. the actual time taken by the car to cover that distance is :
Options: a. 30 minutes, b. 1 hour, c. 2 hours, d. 3 hours, e. none of these
Example Output: b

Example Input: Problem: a can do a piece of work in 16 days. when he had worked for 2 days b joins him. if the complete work was finished in 8 days. in how many days b alone can finish the work ?
Options: a. 18, b. 77, c. 66, d. 55, e. 12
Example Output:
e