I was able to visualize this better by rotating BCD so that it is orientated the same as ABC.
Then it becomes clear that 9.6:6 as 6:CD.
9.6 6
or written differently –––– = ––––
6 CD
Do they still call it
cross-multiplication 9.6 • CD = 6 • 6
36
CD = ––––
9.6
CD = 3.75
.