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: a bag contains 12 red marbles. if someone were to remove 2 marbles from the bag, one at a time, and replace the first marble after it was removed, the probability that neither marble would be red is 25 / 36. how many marbles are in the bag ?
Options: a. 24, b. 48, c. 60, d. 72, e. 84
[EX A]: b

[EX Q]: Problem: an investor deposited $ 10,000 to open a new savings account that earned 12 percent annual interest, compounded quarterly. if there were no other transactions in the account, what was the amount of money in the account 6 months after the account was opened ?
Options: a. $ 10,300, b. $ 10,303, c. $ 10,600, d. $ 10,609, e. $ 10,900
[EX A]: d

[EX Q]: Problem: zinc and copper are melted together in the ratio 9: 11. what is the weight of melted mixture, if 31.5 kg of zinc has been consumed in it ?
Options: a. 58 kg, b. 60 kg, c. 64 kg, d. 70 kg, e. none
[EX A]:
d