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: if x ^ 2 – 3 x = 18, then one possible value of x – 4 =
Options: a. - 9, b. - 5, c. - 3, d. - 1, e. 2
Example Output: e

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: tough and tricky questions: remainders. 1 ^ 1 + 2 ^ 2 + 3 ^ 3 +... + 7 ^ 7 is divided by 7. what is the remainder ?
Options: a. 0, b. 1, c. 2, d. 3, e. 4
Example Output:
e