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: if a - b = 6 and a 2 + b 2 = 50, find the value of ab.
Options: a. a. 7, b. b. 12, c. c. 15, d. d. 18, e. e. 20

Ex Output:
a


Ex Input:
Problem: you have been given a physical balance and 7 weights of 40, 42, 36, 33, 47, 52 and 67 kgs. keeping weights on one pan and object on the other, what is the maximum you can weigh less than 169 kgs.
Options: a. 163, b. 166, c. 162, d. 164, e. 165

Ex Output:
e


Ex Input:
Problem: a thief goes away with a santro car at a speed of 40 kmph. the theft has been discovered after half an hour and the owner sets off in a bike at 60 kmph when will the owner over take the thief from the start ?
Options: a. a. 2, b. b. 5, c. c. 7, d. d. 5, e. e. 1

Ex Output:

e