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 taps a and b can fill a cistern in 12 minutes and 18 minutes respectively. they are turned on at the same time. if the tap a is turned off after 4 minutes, how long will tap b take to fill the rest of the cistern ?
Options: a. 8 min., b. 9 min., c. 10 min., d. 7 min., e. none of these

Ex Output:
a


Ex Input:
Problem: dhoni bought 5 toys with the average cost of $ 10. if david also buys the sixth toy with the price of $ 16, what is the average ( arithmetic mean ) price of those 6 toys ?
Options: a. $ 10, b. $ 7, c. $ 8.5, d. $ 9, e. $ 11

Ex Output:
e


Ex Input:
Problem: when sold at a 70 % discount, a sweater nets the merchant a 40 % profit on the wholesale cost at which he initially purchased the item. by what % is the sweater marked up from wholesale at its normal retail price ?
Options: a. 20 %, b. 40 %, c. 50 %, d. 60 %, e. 78.58 %

Ex Output:

e