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: the first flight out of phoenix airport had a late departure. if the next 3 flights departed on - time, how many subsequent flights need to depart from phoenix on - time, for the airport ' s on - time departure rate to be higher than 40 % ?
Options: a. 4, b. 6, c. 5, d. 2, e. 8
[EX A]: d

[EX Q]: 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
[EX A]: c

[EX Q]: Problem: a group of students decided to collect as many paise from each member of group as is the number of members. if the total collection amounts to rs. 4356, the number of the member is the group is :
Options: a. 57, b. 66, c. 77, d. 87, e. 97
[EX A]:
b