Adding Up Durations (1.15 As 1h15m)

I have been asking this question couple of times but I don't think I am making myself clear. Here it goes again. I am tracking meetings that happend. With other fields, the meeting also has a "Duration "field. in that field how long the meeting lasted is entered. for example if it took 1hour and 15 minutes the user enteres 1.15.

Later, I have a report that displays meeting for selected dates. like the following

1/1/03 1.15
2/2/04 1.30
2/2/02 2.45

I want to add all the duration together for example if we add the above durations we get 5.30 or 5hr30min.
The way I have it not, it sums it up as regular numbers so it sums it up as 4.9

any suggestion would be appreciated.