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: if the simple interest on a certain sum of money for 6 years is one fifth of the sum, then the rate of interest per annum is
Options: a. 3.3 %, b. 7.2 %, c. 6.1 %, d. 5.0 %, e. 3.1 %

Output: a

Input: Consider Input: Problem: a waitress ' s income consists of her salary and tips. during one week, her tips were 3 / 4 of her salary. what fraction of her income for the week came from tips ?
Options: a. 1 / 9, b. 1 / 6, c. 3 / 7, d. 4 / 9, e. 5 / 9

Output: c

Input: Consider Input: Problem: if x is the median of the set { 9 / 2, 11 / 3, x, 28 / 9, 21 / 5 }, x could be
Options: a. 16 / 5, b. 17 / 5, c. 4 / 7, d. 30 / 7, e. 4
Output: e