Task: Question Answering
Input (English): Problem: a can do a piece of work in 10 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 5 days and b leaves after 3 days from the beginning . how long will work lost ? 
Options: a ) 2 , b ) 4 , c ) 5 , d ) 6 , e ) 7
Output (English): d