The easiest way to achieve this is to use parameters rather than filters, but the limitation of parameter is its value can't be updated when your data is reloaded.
In Tableau each worksheet is based on its own underlying table (subset of the total database) - you create that table by placing dimensions and measures on the rows, columns, filter and detail shelves
Conceptually that is very different from the excel concept of bringing values from one sheet to another OK so what
you would create a "Final sheet" and build the calculations you need on that singles sheet (not you can pass filter from sheet to sheet but the dimension needs to be in each sheet's underlying table)
without seeing the actual data I can't be specific but one approach would be using sets to isolate the data in your 2 separate events and then base you summations on those sets
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