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.
Q: Problem: in a 100 m race, sam beats john by 5 seconds. on the contrary, if sam allowed john to start 15 m ahead of sam, then sam and john reach the finishing point at the same time. how long does sam take to run the 100 m race ?
Options: a. 4 seconds, b. 25 seconds, c. 29 seconds, d. 21 seconds, e. 17 seconds
A:
e