Can you add a little bit more about what you are trying to accomplish, and maybe a mockup of your expected results for this data? I'm able to view your workbook but I am not sure what you're trying to visualize here, exactly. What is incorrect about the "INCORRECT AVERAGES" sheet? That sheet is currently showing you the AVG(Quantity) of Smoke and Stacks across the entire data set (across all transactions). If you want it at a daily level, you'll need to include DAY(Date) in the viz -- is this what you're after?
In the first sheet you built, named "Line" you are using the SUM() aggregation, not AVG(), so I'm a bit confused as to what you're after. However, once you get the Level of Detail (what dimensions to include on your visualization, a simple AVG(Measure) should give you what you want.
Happy analyzing with Tableau!