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: by selling 15 pencils for a rupee a man loses 20 %. how many for a rupee should he sell in order to gain 20 % ?
Options: a. 8, b. 7, c. 6, d. 4, e. 10
[A]: e


[Q]: Problem: a train of 25 carriages, each of 60 meters length, when an engine also of 60 meters length is running at a speed of 60 kmph. in what time will the train cross a bridge 1.0 km long ?
Options: a. 2.5, b. 3, c. 5, d. 7, e. 9
[A]: a


[Q]: Problem: circular gears p and q start rotating at the same time at constant speeds. gear p makes 10 revolutions per minute and gear q makes 40 revolutions per minute. how many seconds after the gears start rotating will gear q have made exactly 45 more revolutions than gear p ?
Options: a. 45, b. 80, c. 90, d. 100, e. 120
[A]:
c