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: find the simple interest on rs. 72,000 at 16 2 / 3 % per year for 9 months.
Options: a. 7500, b. 6500, c. 9000, d. 9500, e. none of them
Example Output: c

Example Input: Problem: in traveling from a dormitory to a certain city, a student went 1 / 3 of the way by foot, 3 / 5 of the way by bus, and the remaining 2 kilometers by car. what is the distance, in kilometers, from the dormitory to the city ?
Options: a. 30, b. 45, c. 60, d. 90, e. 120
Example Output: a

Example Input: Problem: a patient is given exactly 750 milliliters of a mixture of two medications daily. medication a contains 40 % pain killer and medication b contains 20 % pain killer. if the patient receives exactly 215 milliliters of pain killer daily, how many milliliters of medication b are in the mixture ?
Options: a. 150, b. 225, c. 325, d. 425, e. 550
Example Output:
d