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 Q]: Problem: set a contains all the even numbers between 2 and 50 inclusive. set b contains all the even numbers between 62 and 110 inclusive. what is the difference between the sum of elements of set b and the sum of the elements of set a ?
Options: a. 1500, b. 3100, c. 4400, d. 6200, e. 7400
[EX A]: a

[EX Q]: Problem: find the simple interest on rs. 72,000 at 16 2 / 3 % per year for 9 months.
Options: a. 7500, b. 6500, c. 9000, d. 9500, e. none of them
[EX A]: c

[EX Q]: Problem: the average of 25 results is 20. the average of first 12 of those is 14 and the average of last 12 is 17. what is the 13 th result ?
Options: a. 128, b. 75, c. 69, d. 78, e. 45
[EX A]:
a