Sum Expression Column

=SUM(ReportItems!Textbox1.Value)

I have an expression column in a table created on my SSRS report.  How can I in turn sum the Expression column?  The expression being used is:

=FIELDS!count.Value/ReportItems!Textbox1.Value

I tried entering in the place where I want this total to go. --- but that throws an error when the page is attempted to run.  And this syntax is at the top of the page, sorry for my silly formatting.