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: a sum of money at simple interest amounts to $ 645 in 3 years and to $ 690 in 4 years. the sum is :
Options: a. $ 153, b. $ 510, c. $ 598, d. $ 549, e. $ 675

A: b
****
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: a bag contains an equal number of one rupee, 50 paise and 25 paise coins respectively. if the total value is 35, how many coins of each type are there ?
Options: a. 20 coins, b. 30 coins, c. 28 coins, d. 25 coins, e. none of these

A:
a
****