If a=2b, 3b=4c, 5c=6d, what is the ratio of a to d?

The answer given in the book is: 16/5

The answer I got is 5/16.

This is how I got my answer, can you tell me where I went wrong?

a=2b

3b=4c

5c=6d

3a=6b=8c

15a=30b=40c=80d

15a=80d

5a=16d

THEREFORE: the ratio of a to do is 5/16