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.

[EX Q]: Problem: excluding stoppages, the average speed of a bus is 60 km / hr and including stoppages, the average speed of the bus is 40 km / hr. for how many minutes does the bus stop per hour ?
Options: a. 18 min, b. 17 min, c. 19 min, d. 20 min, e. 21 min
[EX A]: d

[EX Q]: Problem: if y > 0, ( 9 y ) / 20 + ( 3 y ) / 10 is what percent of y ?
Options: a. 40 %, b. 50 %, c. 60 %, d. 70 %, e. 75 %
[EX A]: e

[EX Q]: Problem: a thief is spotted by a policeman from a distance of 150 meters. when the policeman starts the chase, the thief also starts running. if the speed of the thief be 8 km / hr and that of the policeman 10 km / hr, how far the thief will have run before he is overtaken ?
Options: a. 350 m, b. 200 m, c. 400 m, d. 600 m, e. none of them
[EX A]:
d