Well you can always start by dividing with the simplest number which is two.
Divide as many times as need
Last I checked it was divide 2 from 40, 3 times to get the answer of 5 and then divide 16 the same amount of times for the answer of 2
The answer would be I'm assuming 5 : 2
I said assuming I maybe wrong
Ask a teacher for help if I'm wrong.