Definition: 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: Problem: crazy eddie has a key chain factory. eddie managed to decrease the cost of manufacturing his key chains while keeping the same selling price, and thus increased the profit from the sale of each key chain from 50 % of the selling price to 50 % of the selling price. if the manufacturing cost is now $ 50, what was it before the decrease ?
Options: a. $ 20, b. $ 40, c. $ 50, d. $ 80, e. $ 100
Output:
c