Punch-Time Data. Calculating # of hours worked and # of hours worked alone per shift.

Hello Everyone,
I am trying to calculate the number of hours worked and the number of hours worked alone for each employee's shift. I have attached an example of the database I am working with. The example only contains data for 5 days worth of employee shifts for the same location; however, the database I am working with contains several years' worth of employee shifts for various locations.

I have a feeling that calculating the # of hours worked alone per shift will be WAY harder than calculating the # of hours worked per shift.
Is there a formula I can use to calculate both of these? If not, then will a macro be needed to calculate the harder of the two calculations?

Thanks so much,
Daga3