If A : B = 2 : 3, B : C = 4 : 5 and C : D = 6 : 7, what is the ratio between A to D?

Answer: 
16 : 35
If A : B = 2 : 3, B : C = 4 : 5 and C : D = 6 : 7, what is the ratio between A to D?