Showing subgroup totals

[df123445]

Hi all,

I have a graph showing sales x months.

Once a bar is selected the list of customers is shown in a table but I would like to show the business unit breakdown in a separate table. 

My data is structured in 3 table, one with the group by per month (used for the main chart) 

Another table holds the customer details (connected via year/month to the previous table)

The third table shows to which business unit each customer belongs. 

I connected the last 2 table via customer id, but I can't find the right measure to show the totals by business unit.

Any suggestions? assuming what I just wrote makes any sense. 

Thanks in advance