previous month and average for previous last 3 months

Hi-

I had 2 questions below that I want to either do in power query or power pivot. Can you please help me?

1. I would like to get the previous month for the aban rate in power query. Please see the image below, what formula should I write to get that?

Captur10.PNG


2. In the image below, what formula I should use to calculate in power pivot or power query the rate column for the last 3 months without including the current month and with including the current month.

Capture11.PNG

I apologize for not attaching the file. Please let me know if you could help me with it.