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.

[Q]: Problem: 3 ltr of water is added with 9 ltr of a solution containing 57 % of alcohol in the water. the % of alcohol in the new mixture is ?
Options: a. 41.5 %, b. 42.75 %, c. 43 %, d. 45 %, e. 45.75 %
[A]: b


[Q]: Problem: a man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. the ratio of the speed of the boat in still water and stream is
Options: a. 3: 1, b. 1: 3, c. 2: 4, d. 4: 2, e. none of these
[A]: a


[Q]: Problem: mary and mike enter into a partnership by investing $ 550 and $ 450 respectively. at the end of one year, they divided their profits such that a third of the profit is divided equally for the efforts they have put into the business and the remaining amount of profit is divided in the ratio of the investments they made in the business. if mary received $ 1000 more than mike did, what was the profit made by their business in that year ?
Options: a. $ 8000, b. $ 10000, c. $ 15000, d. $ 12000, e. $ 12500
[A]:
c