Consider two alloys A and B. 50 kg of alloy A is mixed with 70 kg of alloy B. A contains brass and copper in the ratio 3 : 2, and B contains them in the ratio 4 : 3 respectively. What is the ratio of copper to brass in the mixture? A) 8 : 5 B) 7 : 5 C) 5 : 11 D) 4 : 9 E) 5 : 7