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 mixture of 70 litres of milk and water contains 10 % water. how many litres of water should be added to the mixture so that the mixture contains 12 1 / 2 % water ?
Options: a. 2, b. 8, c. 6, d. 3, e. 4
[EX A]: a

[EX Q]: Problem: a cricket player whose bowling average was 21.5 runs per wicket, takes 5 wicket for 52 runs in a match. due to this his average decreases by 0.5. what will be the number of wickets taken by him till the last match ?
Options: a. 64, b. 72, c. 111, d. 721, e. 108
[EX A]: c

[EX Q]: Problem: a solution of 70 litres contains oil and water in the ratio 9: x. if 6 litres of water is added to the solution, the ratio becomes 6: 4, find the value of x ?
Options: a. 6, b. 8.5, c. 9, d. 6.5, e. 5
[EX A]:
e