VBF syntax for SSRS expression cannot figure out proper construct

Question

looking for help on what should be a very basic function. I am trying to get a SUM of a specific value, however I do not seem to get the syntax correct.

Here is what I have

=Sum(Fields!PriorYearSalesDollars.Value - Sum(Fields!PriorYearCost.Value           
+Sum(Fields!PriorYearFrtCost.Value)))

However I get an error when trying to sum. Is there another way to test this also? Each time I modify the expression I then have to save the report and upload to the report server and test again. If I do it through the preview function in visual studio it throws a generic error on the whole report. When running from report server, just this specific column shows #Error

Answer 1

This is the syntax that works after FIRST changing the column format to numbers where I accidentally did it as currency first. Not sure why currency didn't work, but this is correct.

=Sum(Fields!PriorYearSalesDollars.Value) - (Sum(Fields!PriorYearCost.Value) +   Sum(Fields!PriorYearFrtCost.Value))