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.

Input: Consider Input: Problem: two trains of equal length are running on parallel lines in the same directions at 46 km / hr. and 36 km / hr. the faster trains pass the slower train in 72 seconds. the length of each train is :
Options: a. 82 m, b. 50 m, c. 72 m, d. 100 m, e. none of these

Output: d


Input: Consider Input: Problem: two taps a and b can fill a cistern in 12 minutes and 18 minutes respectively. they are turned on at the same time. if the tap a is turned off after 4 minutes, how long will tap b take to fill the rest of the cistern ?
Options: a. 8 min., b. 9 min., c. 10 min., d. 7 min., e. none of these

Output: a


Input: Consider Input: Problem: find remainder if ( 67 ^ 67 + 67 ) is divided by 68
Options: a. 60, b. 62, c. 66, d. 72, e. 78


Output: c