Tax Status of RMD calculations for both pre-tax and after-tax IRAs

Hello - First, thanks for doing this!

I have 3 IRAs: a Roth,  pre-tax Rollover and after tax Traditional.I will need to take my RMD starting next year. I understand that no distribution is required from the Roth. For the other two plans, how is that handled and how do I calculate how much is taxable vs non-taxable from the RMD?