Rolling Totals For Several Weeks

I have an excel sheet setup with several tabs which are organized by work days in a week. (i.e. aug 18, aug 19, aug 20, aug 21, aug22, aug 25, aug 26, aug 27, aug 28, aug 29) Sample file has been included.

I would like to do a rolling total of 1 particular cell (the same location on all the sheets, i.e. cell a2 on all sheets) for the past 4 weeks, and it automatically adjusts itself based on today's date (i.e. today is august 27, it will total everything from jul 30, 31, aug 1, 4, 5, 6, 7, 8, 11, 12, 13, 14, 15, 18, 19, 20, 21, 22, 25, 26.).

Is it possible to do this?

I am not familiar with VBA or Macros, so solutions using either of these will require some detailed explanation for me to understand how to apply them.