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: michelle deposited a certain sum of money in a savings account on july 1 st, 2007. she earns an 14 % interest compounded semiannually. the sum of money in the account on december 31 st, 2009 is approximately what percent of the initial deposit ?
Options: a. 117 %, b. 120 %, c. 121 %, d. 138 %, e. 145 %
Example Output: d

Example Input: Problem: a train 50 m long takes 6 sec to cross a man walking at 5 kmph in a direction opposite to that of the train. find the speed of the train ?
Options: a. 15 kmph, b. 25 kmph, c. 35 kmph, d. 45 kmph, e. 55 kmph
Example Output: b

Example Input: Problem: the average speed of a car is 1 4 / 5 times the avg speed of a bike. a tractor covers 575 km in 23 hrs. how much distance will the car cover in 4 hrs if the speed of the bike is twice speed of the tractor ?
Options: a. 300 km, b. 320 km, c. 360 km, d. 390 km, e. 400 km
Example Output:
c