The number of CDs is 36.

The factors form of .

The different ways Clara organize 36 CDs on each self, at least 4 per shelf and at least 2 shelves of CDs as follows:

So, the CDs can be organized as 4 CDs on 9 shelves.

So, the CDs can be organized as 6 CDs on 6 shelves.

So, the CDs can be organized as 9 CDs on 4 shelves.

So, the CDs can be organized as 12 CDs on 3 shelves.

So, the CDs can be organized as 18 CDs on 2 shelves.