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.

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
d

Problem: the sector of a circle has radius of 24 cm and central angle 135 o. find its perimeter ?
Options: a. 91.5 cm, b. 11.5 cm, c. 104.6 cm, d. 92.5 cm, e. 99.5 cm
c

Problem: what is the median of a set of consecutive integers if the sum of nth number from the beginning and nth number from the end is 110 ?
Options: a. 10, b. 25, c. 55, d. 75, e. 100

c