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.

Example 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
Example Output: e

Example Input: Problem: what is the value of n if the sum of the consecutive odd intergers r from 1 to n equals 169 ?
Options: a. 47, b. 25, c. 37, d. 33, e. 29
Example Output: b

Example Input: Problem: a dress on sale in a shop is marked at $ d. during the discount sale its price is reduced by 45 %. staff are allowed a further 40 % reduction on the discounted price. if a staff member buys the dress what will she have to pay in terms of d ?
Options: a. 0.35 d, b. 0.76 d, c. 0.65 d, d. 0.77 d, e. 0.33 d
Example Output:
e