Task: Question Answering
Input (English): Problem: a jar contains a mixture of a & b in the ratio 4 : 1 . when 10 l of mixture is replaced with liquid b , ratio becomes 2 : 3 . how many liters of liquid a was present in mixture initially . 
Options: a ) 12 , b ) 15 , c ) 16 , d ) 20 , e ) 25
Output (English): c