[Orgmode] Easiest way to calculate time spent

[Rainer Hansen]

Hi,

I am new to Org-Mode and I have written a number of project tasks in the 
following form:

* Project
** Task 1
    <2009-03-19 Thu 13:15-13:35>
    Description of Task 1
** Task 2
    <2009-03-18 Wed 12:15-13:35>
    Description of Task 2
** Task 3
     SCHEDULED: <2009-03-11 Wed 19:55-21:45> CLOSED: [2009-03-12 Thu 23:29]
     Result of Task 3

For task 3 the time calculated should be 2009-03-11 19:55-21:45 that mean 1:50 
hours.

I have quite a number of items and I wonder if there is an easy way to sum up 
all the time spent on the project (similar to what you can do with clocked 
items)? 

Thanks for your help!

Regards,
Rainer

P.S. I love Org-Mode - it is great!