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: a sum of money at simple interest amounts to rs. 720 after 2 years and to rs. 1020 after a further period of 5 years. the sum is :
Options: a. 400, b. 500, c. 600, d. 700, e. 800

Ex Output:
c

Ex Input:
Problem: a can do a piece of work in 4 hours; b and c together can do it in 3 hours, while a and c together can do it 2 hours. how long will b alone take to do it ?
Options: a. 8 hours, b. 10 hours, c. 12 hours, d. 24 hours, e. none of these

Ex Output:
c

Ex Input:
Problem: a " palindromic integer " is an integer that remains the same when its digits are reversed. so, for example, 43334 and 516615 are both examples of palindromic integers. how many 6 - digit palindromic integers are both even and greater than 500000 ?
Options: a. 160, b. 200, c. 240, d. 300, e. 480

Ex Output:
b