How can I make the value of "3" in the following function reference a
cell, so that I can change the value and recalculate my results.
=SUMPRODUCT(N($A$48:$A$5559="R"),N($L$48:$L$5559="3"))

Hello,
Testing with Excel, I believe if you change "3" to a cell reference
like A11 (or $A$11 to make it absolute) then you get what you are
seeking.

So =SUMPRODUCT(N($A$48:$A$5559="R"),N($L$48:$L$5559=$A$11)) should work.

Google is the best.