If I've understood correctly, you're asking how to reference the textbox containing the total work hours value so that you can convert it to hours and minutes using an expression in a different textbox?
You can use either ReportItems! e.g.
=ReportItems!Textbox20.Value)
or ReportItems("") e.g.
=ReportItems("Textbox20").Value
to reference the value of another textbox. Be careful with the names as they are case sensitive.