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.

[EX Q]: Problem: raman mixed 48 kg of butter at rs. 150 per kg with 36 kg butter at the rate of rs. 125 per kg. at what price per kg should he sell the mixture to make a profit of 40 % in the transaction ?
Options: a. 129, b. 287, c. 195, d. 188, e. 112
[EX A]: c

[EX Q]: Problem: the speed of a boat in still water is 15 km / hr and the rate of current is 3 km / hr. the distance travelled downstream in 24 minutes is
Options: a. 17.2 km, b. 7.2 km, c. 7.6 km, d. 17.6 km, e. 27.2 km
[EX A]: b

[EX Q]: Problem: subash can copy 50 pages in 10 hrs. subash and prakash together can copy 300 pages in 40 hours. in how much time prakash can copy 20 pages.
Options: a. 8, b. 10, c. 12, d. 14, e. 16
[EX A]:
a