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: Consider Input: Problem: a bag contains 10 green and 8 white balls. if two balls are drawn simultaneously, the probability that both are of the same colour is
Options: a. 8 / 15, b. 21 / 44, c. 3 / 5, d. 11 / 15, e. 7 / 15

Output: b


Input: Consider Input: Problem: 54671 - 14456 - 31466 = ?
Options: a. 2449, b. 5449, c. 8749, d. 8449, e. 6468

Output: c


Input: Consider Input: Problem: on a certain date, pat invested $ 7,000 at x percent annual interest, compounded annually. if the total value of the investment plus interest at the end of 10 years will be $ 28,000, in how many years total will the total value of the investment plus interest increase to $ 56,000 ?
Options: a. 15, b. 16, c. 18, d. 20, e. 24


Output: a