Task: Question Answering
Input (English): Problem: if 3 people a , b , c can do a work simultaneously in 6 days . a and b can do work in 10 days . b and c can do work in 15 days . c and a can do the same work in 20 days . in how many days that a can complete the same work alone ? 
Options: a ) 20 , b ) 25 , c ) 30 , d ) 24 , e ) 19
Output (English): d