How to automatically select specific buyers and add only their purchases in calc

In my spreadsheet are a number of columns,including ‘purchase (column b), date (column d), buyer (column e), etc’. I can use the find all function to see everything buyer Bill has purchased and it shows the search results. However, I want to use a formula or a function to actually add the total - purchase (Column b) of all that specific buyer without going to each line and separately adding the purchase. How can I do this? Thank you. I have 2 screenshots to demonstrate the question but don’t know how to attach them?

Check the wiki on SUMPRODUCT

https://wiki.documentfoundation.org/Documentation/Calc_Functions/SUMPRODUCT

I guess you will need something like
=SUMPRODUCT(B2:B100; E2:E100="Bill")
and for your automatically replace ="Bill" with a reference to a cell, where you input the name (Maybe even use a dropdown with data valitidy for this.)

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