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: the mean proportional between 4 and 16 is ?
Options: a. 12, b. 13, c. 14, d. 15, e. 16

Output: e

Input: Consider Input: Problem: a walks at 10 kmph and 4 hours after his start, b cycles after him at 20 kmph. how far from the start does b catch up with a ?
Options: a. 100 km, b. 150 km, c. 80 km, d. 120 km, e. 200 km

Output: c

Input: Consider Input: Problem: jack and christina are standing 240 feet apart on a level surface. their dog, lindy, is standing next to christina. at the same time, they all begin moving toward each other. jack walks in a straight line toward christina at a constant speed of 5 feet per second and christina walks in a straight line toward jack at a constant speed of 3 feet per second. lindy runs at a constant speed of 9 feet per second from christina to jack, back to christina, back to jack, and so forth. what is the total distance, in feet, that lindy has traveled when the three meet at one place ?
Options: a. 180, b. 210, c. 240, d. 270, e. 300
Output: d