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.
--------
Question: Problem: the ` ` racing magic ' ' takes 120 seconds to circle the racing track once. the ` ` charging bull ' ' makes 40 rounds of the track in an hour. if they left the starting point together, how many minutes will it take for them to meet at the starting point for the second time ?
Options: a. 3, b. 6, c. 9, d. 12, e. 15

Answer: d


Question: Problem: walking at 4 / 5 of her normal speed, a worker is 10 minutes later than usual in reaching her office. the usual time ( in minutes ) taken by her to cover the distance between her home and her office is
Options: a. 30, b. 35, c. 40, d. 45, e. 50

Answer: c


Question: Problem: if 2 x = 3 y = 10, then 15 xy = ?
Options: a. 1,200, b. 200, c. 120, d. 40, e. 250

Answer:
e