Summary (hours) of selected rows in work view!

If i have more rows and would like to just know the current effort i did on this project excluding already invoiced items I expected to select and mark my number of rows and see a kind of summary at the bottom page.

In my case for instance (see also attachment) = 48 hours (selected)!

I have to export it into excel if i even have more rows than in this example.

Requirement: The two numbers of estimated and worked hours at the bottom page should be extended with a third number "Selected hours"!

Thanks and many regards.

Martin