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.

[Q]: Problem: cost is expressed by the formula tb ^ 4. if b is doubled, the new cost w is what percent of the original cost ?
Options: a. w = 200, b. w = 600, c. w = 800, d. w = 1600, e. w = 50
[A]: d


[Q]: Problem: water is leaking out from a cylinder container at the rate of 0.31 m ^ 3 per minute. after 10 minutes, the water level decreases 1 / 9 meters. what is value of the radius in meters ?
Options: a. 2, b. 3, c. 4, d. 6, e. 9
[A]: b


[Q]: Problem: what is the probability that the sum of two dice will yield a 5, and then when both are thrown again, their sum will again yield a 5 ? assume that each die has 4 sides with faces numbered 1 to 4.
Options: a. 1 / 144, b. 1 / 36, c. 1 / 12, d. 1 / 16, e. 1 / 3
[A]:
d