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.

Example Input: Problem: what sum of money will produce rs. 80 as simple interest in 4 years at 3 1 / 2 percent ?
Options: a. 263, b. 571.4, c. 367, d. 368, e. 339
Example Output: b

Example Input: Problem: together, 15 type a machines and 7 type b machines can complete a certain job in 4 hours. together 8 type b machines and 15 type c machines can complete the same job in 11 hours. how many q hours would it take one type a machine, one type b machine, and one type c machine working together to complete the job ( assuming constant rates for each machine. ?
Options: a. 22 hours, b. 30 hours, c. 44 hours, d. 60 hours, e. it can not be determined from the information above.
Example Output: c

Example Input: Problem: two trains leave a station traveling the same direction. train a leaves the station traveling at a constant speed of 60 mph, and train b leaves the station traveling at a constant speed of 80 mph. if both trains maintain constant speeds, in how many minutes will train b overtake train a if train a left 40 minutes prior to train b ?
Options: a. 90, b. 100, c. 110, d. 120, e. 130
Example Output:
d