Crystal Reports Adding Total Times

Message

   Hi I am still new with Crystal Reports and I am working on a report that lists all cases performed in a room, and the duration of each case

I need to have a summary totaling the number of cases and the total time for all cases. I can't seem to be able to add the times. 

Data:
Room: OR2
Case  Date            Case duration
123    4/10/2012    1:30
786    4/10/2012    4:15
369    4/11/2012    0:58

I need it to sumarize at the end of each room to show:

Total OR2:  3 cases performed in 6h43min

I got the number of cases but I need help in adding the duration times.

Thanks for any tips!

Cheers,
B