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: a man bought an article and sold it at a gain of 5 %. if he had bought it at 5 % less and sold it for re 5 less, he would have made a profit of 10 %. the c. p. of the article was
Options: a. 960, b. 980, c. 900, d. 970, e. 1000
Example Output: e

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: in 1950, richard was 4 times as old as robert. in 1955, richard was 3 times as old as robert. in which year was richard 1.5 times as old as robert ?
Options: a. 1960, b. 1965, c. 1970, d. 1975, e. 2000
Example Output:
e