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: the perimeter of an isosceles right triangle is 12 + 12 sq rt 2. what is the length of the hypotenuse of the triangle ?
Options: ['a. 5', 'b. 6', 'c. 7', 'd. 8.485', 'e. 8']
[EX A]: d

[EX Q]: Problem: mary works in a restaurant a maximum of 70 hours. for the first 20 hours, she is paid $ 8 per hour. for each overtime hour, she is paid at a rate which is 25 % higher than her regular rate. how much mary can earn in a week ?
Options: a. 600, b. 620, c. 660, d. 320, e. 400
[EX A]: c

[EX Q]: Problem: how many liters of pure alcohol must be added to a 100 - liter solution that is 20 percent alcohol in order to produce a solution that is 40 percent alcohol ?
Options: a. 7 / 2, b. 5, c. 100 / 3, d. 8, e. 39 / 4
[EX A]:
c