pull data from 2 different tables into 1 table

Hello. I am trying to pull data from data from 2 different tables into table. 

1st table :  ON HAND inventory which included all sales and purchase receipts. returns . gives me real on hand qty. I get my on hand after I sum all the transcations.

2nd table with just sales last 90D sales. monthly average (90d sales/3) with measure.

I want to build a table with 3 columns

1. items

2. on hand qty 

3. sales Average 

I am only only able to pull items with Summerize formula. How can I pull on final on hand qty by an item which will be sum of all tranctions in the 1st table  and Average by an item from second table?

Thank you