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Now that we've created the new sub-data set we need to create some room in the existing table to add the new data.
Select the table and right click on the row handle for the detail row and select Insert|Row|Below to add a new row below the current detail row, this way the sale details for each property will be listed below the address.
Then we merge the cells together by clicking and dragging across the visible cells in the new row
and then right clicking in the selected cells and selecting Merge Cells from the menu 
This way when we add the new data set to the existing table it'll fill up the width of the parent table. You don't have to do it this way, and you may find better methods of laying out your report pages, but this is to demonstrate linking data sets, not how to layout pages.