Task: Question Answering
Input (English): Problem: an alloy of copper and zinc contains copper and zinc in the ratio 5 : 4 . another alloy of copper and zinc contains copper and zinc in the ratio 3 : 6 . in what ratio should the two alloys be mixed so that the resultant alloy contains equal proportions of copper and zinc ? 
Options: a ) 4 : 1 , b ) 6 : 1 , c ) 1 : 3 , d ) 2 : 1 , e ) 4 : 1
Output (English): c