help with empirical formula question? thanks

here are the answers

Attachment not found

I have no idea how to get that answer ;s
exam on thursdy

thnx v much for any help

there are three metals (whose ratio does not change) and oxygen.

You are told that only the oxidation state of the copper changes by -1 and there are 3 copper atoms.

The only way to compensate for this is by loss of oxygen atoms (one for every two copper atoms)

Can you see where to go?