Task: Question Answering
Input (English): Problem: ram , who is half as efficient as krish , will take 21 days to complete a task if he worked alone . if ram and krish worked together , how long will they take to complete the task ? 
Options: a ) 16 days , b ) 12 days , c ) 8 days , d ) 7 days , e ) 18 days
Output (English): d