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: how many quarters are equal to 7 dollars ?
Options: a. 1, b. 28, c. 12, d. 9, e. 7
Example Output: b

Example Input: Problem: a trader mixes 80 kg of tea at 15 per kg with 20 kg of tea at cost price of 20 per kg. in order to earn a profit of 25 %, what should be the sale price of the mixed tea ?
Options: a. 23.75, b. 22, c. 20, d. 19.20, e. none of these
Example Output: c

Example Input: Problem: in an examination, a student scores 4 marks for every correct answer and loses 1 mark for every wrong answer. if he attempts all 200 questions and secures 240 marks, the number of questions he attempts incorrectly, is :
Options: a. 135, b. 200, c. 140, d. 112, e. 48
Example Output:
d