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 train 150 m long is running at a speed of 68 kmph. how long does it take to pass a man who is running at 8 kmph in the same direction as the train ?
Options: a. 2 sec, b. 6 sec, c. 8 sec, d. 9 sec, e. 5 sec
Example Output: d

Example Input: Problem: the price of a book is increased from $ 300 to $ 390. what is the % of increase in its price ?
Options: a. 10 %, b. 20 %, c. 30 %, d. 35 %, e. 45 %
Example Output: c

Example Input: Problem: raja spends 35 % of his monthly income on household items, 20 % of his monthly income on buying cloths, 5 % of his monthly income on medicines and saves the remaining amount which is rs. 15000. find his monthly income.
Options: a. rs. 40000, b. rs. 36000, c. rs. 37500, d. rs. 45000, e. none of these
Example Output:
c