Task: Question Answering
Input (English): Problem: a and b invests rs . 3500 and rs . 4000 respectively in a business . if a doubles his capital after 6 months . in what ratio should a and b divide that year ' s profit ? 
Options: a ) 21 : 5 , b ) 21 : 16 , c ) 21 : 2 , d ) 9 : 9 , e ) 21 : 11
Output (English): b