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: if i walk at 4 km / h, i miss the bus by 10 minutes. if i walk at 5 km / h, i reach 5 minutes before the arrival of the bus. how far i walk to reach the bus stand ?
Options: a. 5 km, b. 4.5 km, c. 5 1 4 km / h, d. can not be determined, e. none of these
A:
a