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: a shopkeeper buys mangoes at the rate of 5 a rupee and sells them at 2 a rupee. find his net profit or loss percent ?
Options: a. 34 %, b. 30 %, c. 50 %, d. 150 %, e. 33 %
[EX A]: d

[EX Q]: Problem: 3 numbers are in the ratio 3: 5: 7. the largest number value is 70. find difference between smallest & largest number is ?
Options: a. 40, b. 45, c. 35, d. 30, e. 50
[EX A]:
a