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 11 % stock yields 8 %. the market value of the stock is :
Options: a. rs. 72, b. rs. 137.50, c. rs. 112.50, d. rs. 116.50, e. none of these
Example Output: b

Example Input: Problem: a fort had provision of food for 150 men for 45 days. after 15 days, 10 men left the fort. the number of days for which the remaining food will last, is :
Options: a. 32, b. 37 1 / 4, c. 42, d. 54, e. 45
Example Output: a

Example Input: Problem: the average marks of a class of 40 students is 44 and that of another class of 45 students is 70. find the average marks of all the students ?
Options: a. 52.6, b. 52.4, c. 52.1, d. 69.5, e. 52.9
Example Output:
d