X and Y are the two alloys which were made by mixing Zinc and Copper in the ratio 6 : 9 and 7 : 11 respectively. If 40 grams of alloy X and 60 grams of alloy Y are melted and mixed to form another alloy Z, what is the ratio of Zinc and Copper in the new alloy Z?

Alloy X has zinc and copper in ratio 6:9

If 40 grams is taken then weights of zinc and copper are: 

Zinc = $$\frac{6}{15}$$ * 40 = 16 grams

Copper = $$\frac{9}{15}$$ * 40 = 24 grams

Alloy Y has zinc and copper in ratio 7:11

If 60 grams is taken then weights of zinc and copper are: 

Zinc = $$\frac{7}{18}$$ * 60 = $$\frac{70}{3}$$ grams

Copper = 60 - $$\frac{70}{3}$$ = $$\frac{110}{3}$$ grams

When mixed together, the weights of Zinc and Copper are:

Zinc = 16 + $$\frac{70}{3}$$ = $$\frac{118}{3}$$

Copper = 24 + $$\frac{110}{3}$$ = $$\frac{182}{3}$$

Ratio = 118/3:182/3 = 59:91