Adding stock Opening balance to a custom report that shows total sales made and closing balance as well

Good day

I am trying to come up with a report that shows my opening stock balance for a period and the total sales made to a customer (quantity wise) and then the closing balance.

Which table can I use to get the opening stock balance for a specific period?

I am working in the Report designer , I have used the table “INItemSiteHist” table , it only picks one line item instead of stock from all the fields for the respective stock item.

I have attached the report I am