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: a train covers a distance of 100 km in 1 hour. if its speed is decreased by 15 km / hr, the time taken by the car to cover the same distance will be ?
Options: a. 1 hr, b. 1 hr 10 min, c. 50 min, d. 1 hr 30 min, e. 1 hr 45 min
[A]: b


[Q]: Problem: what is the value of n if the sum of the consecutive odd intergers r from 1 to n equals 169 ?
Options: a. 47, b. 25, c. 37, d. 33, e. 29
[A]: b


[Q]: Problem: what is the length of a bridge ( in meters ), which a train 156 meters long and travelling at 45 km / h can cross in 30 seconds ?
Options: a. 203, b. 211, c. 219, d. 227, e. 235
[A]:
c