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.

Input: Consider Input: Problem: there are 15 balls in a jar. you take out 3 blue balls without putting them back inside, and now the probability of pulling out a blue ball is 1 / 3. how many blue balls were there in the beginning ?
Options: a. 12., b. 9., c. 8., d. 7., e. 6.

Output: d


Input: Consider Input: Problem: a is twice as good a work man as b and together they finish the work in 4 days. in how many days a alone can finish the work ?
Options: a. 3, b. 2, c. 7, d. 9, e. 6

Output: e


Input: Consider Input: Problem: 4 liters of a 20 percent solution of alcohol in water are mixed with 5 liters of a 10 percent alcohol in water solution. what is the percentage of alcohol in the new solution ?
Options: a. 14.4 %, b. 14.8 %, c. 15.2 %, d. 15.6 %, e. 16.0 %


Output: a