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: the total marks obtained by a student in mathematics and physics is 50 and his score in chemistry is 20 marks more than that in physics. find the average marks scored in mathamatics and chemistry together.
Options: a. 15, b. 25, c. 35, d. 45, e. 55
Example Output: c

Example Input: Problem: if a train, travelling at a speed of 90 kmph, crosses a pole in 4 sec, then the length of train is ?
Options: a. 281, b. 125, c. 288, d. 100, e. 121
Example Output: d

Example Input: Problem: company c sells a line of 25 products with an average retail price of $ 1,200. if none of these products sells for less than $ 400, and exactly 10 of the products sell for less than $ 1,000, what is the greatest possible selling price of the most expensive product ?
Options: a. 12000, b. 13000, c. 14000, d. 15000, e. 16000
Example Output:
a