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 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: when positive integer n is divided by 3, the remainder is 1. when n is divided by 7, the remainder is 5. what is the smallest positive integer k such that k + n is a multiple of 21 ?
Options: a. 2, b. 4, c. 6, d. 8, e. 10

Output: a

Input: Consider Input: Problem: when sold at a 70 % discount, a sweater nets the merchant a 40 % profit on the wholesale cost at which he initially purchased the item. by what % is the sweater marked up from wholesale at its normal retail price ?
Options: a. 20 %, b. 40 %, c. 50 %, d. 60 %, e. 78.58 %
Output: e