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 Input:
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 Output:
e


Ex Input:
Problem: if the average ( arithmetic mean ) of a and b is 45 and the average of b and c is 80, what is the value of c − a ?
Options: a. 25, b. 60, c. 90, d. 140, e. it can not be determined from the information given.

Ex Output:
b


Ex Input:
Problem: danny and steve are running towards each other, each one from his own house. danny can reach steve ' s house in 25 minutes of running, which is half the time it takes steve to reach danny ' s house. if the two started to run at the same time, how much time longer will it take steve to reach the halfway point between their houses than danny to reach the halfway point between their houses ?
Options: a. 12.5 minutes., b. 25 minutes, c. 35 minutes., d. 35 minutes, e. 75 minutes

Ex Output:

a