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 Input:
Problem: a train 510 m long is running at a speed of 45 km / hr. in what time will it pass a bridge 140 m long ?
Options: a. 40, b. 52, c. 26, d. 21, e. 14

Ex Output:
b

Ex Input:
Problem: a theater box office sold an average ( arithmetic mean ) of 63 tickets per staff member to a particular movie. among the daytime staff, the average number sold per member was 78, and among the evening staff, the average number sold was 60. if there are no other employees, what was the ratio of the number of daytime staff members to the number of evening staff members ?
Options: a. 2: 3, b. 1: 4, c. 1: 5, d. 6: 11, e. 4: 7

Ex Output:
c

Ex Input:
Problem: a snooker tournament charges $ 45.00 for vip seats and $ 20.00 for general admission ( " regular " seats ). on a certain night, a total of 320 tickets were sold, for a total cost of $ 7500. how many fewer tickets were sold that night for vip seats than for general admission seats ?
Options: a. 200, b. 276, c. 230, d. 240, e. 250

Ex Output:
b