Detailed Instructions: In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.
Problem:Problem: a mixture of 50 litres of milk and water contains 10 % water . how many litres of water should be added to the mixture so that the mixture contains 15 % water ? 
Options: a ) 15 , b ) 20 , c ) 25 , d ) 30 , e ) 10
Solution:
c