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: a train 510 m long is running at a speed of 45 km / hr. in what time will it pass a bridge 140 m long ?
Options: a. 40, b. 52, c. 26, d. 21, e. 14
Example Output: b

Example Input: Problem: if a and b are the roots of the equation x 2 - 9 x + 9 = 0, then the value of a 2 + b 2 is :
Options: a. 63, b. 24, c. 17, d. 6, e. 5
Example Output: a

Example Input: Problem: solve below question 2 x + 1 = - 19
Options: a. - 8, b. - 9, c. 9, d. 8, e. - 10
Example Output:
e