Task: Question Answering
Input (English): Problem: a can do a piece of work in 15 days and b can do it in 15 days and c can do it 20 days . they started the work together and a leaves after 2 days and b leaves after 4 days from the beginning . how long will work lost ? 
Options: a ) 15 , b ) 10 , c ) 12 , d ) 11 , e ) 13
Output (English): c