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: 108 ã — 108 + 92 ã — 92 = ?
Options: a. 20120, b. 11500, c. 20128, d. 20660, e. 20228

Output: c


Input: Consider Input: Problem: at what rate percent per annum will a sum of money double in 6 years.
Options: a. 12.5 %, b. 13.5 %, c. 11.5 %, d. 14.5 %, e. 16.6 %

Output: e


Input: Consider Input: Problem: a sum of money becomes 7 / 6 of itself in 7 years at a certain rate of simple interest. the rate per annum is ?
Options: a. 50 / 13, b. 50 / 17, c. 50 / 19, d. 50 / 21, e. 50 / 23


Output: d