Task: Question Answering
Input (English): Problem: a milk man has 10 liters of milk . if he mixes 5 liters of water , which is freely available , in 20 liters of pure milk . if the cost of pure milk is rs . 18 per liter , then the profit of the milkman , when he sells all the mixture at cost price is : 
Options: a ) 20 % , b ) 15 % , c ) 33.33 % , d ) 18 % , e ) none of these
Output (English): b