how can i write the Lookup functions please

Hi david_flu 

You did not mention how to calcualte the sales amount but I am assuming it is unit price * kg. If so, try this calc column in your first table:

Sales =
VAR __UNIT_PRICE =
    LOOKUPVALUE (
        'table2'[Unit Price],
        'table2'[Regions], 'table1'[Store],
        'table2'[Product], 'table1'[Regions]
    )
RETURN
    __UNIT_PRICE * 'Table1'[KGs]

If this isn't what you're looking for, please elaborate your use case and provide a sample data we can easily copy-paste (not an image) as well as your sample result.  Please refer to this sticky post when creating new posts in the future: https://community.fabric.microsoft.com/t5/Desktop/How-to-Get-Your-Question-Answered-Quickly/m-p/3332479#M1112153 

Daniel_PowerBI the solution danextian should work and you can also do this:

add 2 new columns in each table and then set the relationship on these new columns, which will be one to many, one will be on the store/product side table. 

//add new column in Sales Table
Surrogate Key = SalesTable[Store] & SalesTable[Product]

//add new column in Store Product table
Surrogate Key = StoreProductTable[Store] & StoreProductTable[Product]

//add new measure for sales
Sales Measure = 
SUMX (  SalesTable, SalesTable[Product Sales] & RELATED ( StoreProductTable[Unit Price] ) )

and to visualize. use Week/Day/Store column from SalesTable and the measure Sales Measure

Change the column names and table names as per your data model.