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: the overall age of x and y is 19 year greater than the overall age of y and z. z is how many decades younger that x ?
Options: a. 11, b. 15, c. 12, d. 19, e. 20
[EX A]: d

[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

[EX Q]: Problem: the h. c. f of two numbers is 23 and the other two factors of their l. c. m are 14 and 15. the larger of the two numbers is :
Options: a. 338, b. 278, c. 345, d. 231, e. 121
[EX A]:
c