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: two trains travel in opposite directions at 36 kmph and 45 kmph and a man sitting in slower train passes the faster train in 8 seconds. the length of the faster train is
Options: a. 80 m, b. 100 m, c. 120 m, d. 180 m, e. 160 m

Ex Output:
b

Ex Input:
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 Output:
d

Ex Input:
Problem: a and b together can do a piece of work in 1 days. if a alone can do the same work in 20 days, then b alone can do the same work in ?
Options: a. 0.35 days, b. 0.45 days, c. 0.55 days, d. 0.25 days, e. 0.95 days

Ex Output:
e