You have asked several question
"Can I create a variable for data entry and then reference that in my calculations?
Yes use a parameter - then create a calculation sum(value)*[Enter Last Quarter Completed]
how would I determine the last qtr being displayed for the year, and then automatically calculate?
this will find the last quarter in the view
then you can use it in a case statement to get your multiplication value and drop that in your formula (s)
it would return something like this
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