Average Man Days per month

Hi,

I'm new on PowerBI, and I'm struggling to do the following, which is however pretty simple on excel:

•  I've got a table AllActivitiesCSV which contains the list of activities the people of my team are working on. The Project Delivery name is mentioned in those activities when they are working on one (see picture here after):

   

   

• I've got another table "PowerBI-Deliveries" which contains the list of the Delivery projects, the End Date of the project (when empty it means the project is still active), and the PS Days which may have been ordered

   

   

• What i'd like to do is get the number of days spent on each of the finished project, calculated with an average on a monthly basis
• I'd like also to take into account the PS Days ordered. For instance, if Delivery A has 10 PS days ordered, and we have spent 15 working on it, then i'd like to get 5 as a result

Since screenshot talks better than text, the final graph i'm aiming at is the following one, which has the average man days of the ended project, on a monthly basis.

I'd be very happy if anyone could help me !

Thank you,

Nicolas