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.

Input: Consider Input: Problem: two trains are moving in opposite directions at 60 km / hr and 90 km / hr. their lengths are 1.15 km and 0.6 km respectively. the time taken by the slower train to cross the faster train in seconds is ?
Options: a. 42, b. 9, c. 7, d. 67, e. 15

Output: a

Input: Consider Input: Problem: if a = 105 and a ^ 3 = 21 25 45 z, what is the value of z ?
Options: a. 35, b. 42, c. 45, d. 49, e. 54

Output: d

Input: Consider Input: Problem: if i walk at 6 km / h, i miss the bus by 12 minutes. if i walk at 5 km / h, i reach 14 minutes before the arrival of the bus. how far i walk to reach the bus stand ?
Options: a. 13 km, b. 12 km, c. 11 km, d. 6.5 km, e. 5.5 km
Output: a