Task: Question Answering
Input (English): Problem: in what ratio must water be mixed with milk to gain 16 ( 2 / 3 ) % on selling the mixture at cost price ? 
Options: a ) 1 : 6 , b ) 6 : 1 , c ) 2 : 3 , d ) 4 : 3 , e ) 3 : 2
Output (English): a