Three vessels having volumes in the ratio of 1:2:3 are full of a mixture of coke and soda.In the first vessel ratio of coke and soda is 2:3 , in the second 3:7, and in third 1:4.If the liquid in all the three vessels were mixed in a bigger container, then the resulting ratio of coke and soda is..

The answer is 4:11. But I am not getting how to get it.