PLEASE HELP!!! CRYSTAL REPORTS TOTAL DURATIONS

I have an application which is linked to a database. The Database is very simple, only 3 fields, which are Date, Task, duration.

I am using Crystal Reports to create summary reports of the data.

The report looks something like below (Example):

Date                                                     Task                                          Duration

18/03/06                                     Meeting                              01:00:59

19/03/06                                     Lecture                               01:01:56

19/03/06                                     Lab                                     02:02:01

At the bottom of the report, under the Duration field I want to have the Total Duration. I can't seem to do this. Can anybody help please?

Thanks