Getting sum of Timespent from all the related Task Workitems

Hi,

In one of the project, they use tasks to capture the Service Requests(SR) and in the Time Code they have all the steps for the Service Request. When a SR is worked on by the owner he chooses the appropriate time code to capture the time spent. When the SR is completed by owner he closes the SR.
But After closure if it is required to do some more additional work on the SR then they create one more tasks with the SR description and use the related link.

There can be more than one task which are related in this manner.
Eg: taskA related to taskB
taskB related to taskC
taskA related to taskD
If you look at this example we can understand that all of these tasks are related.
I am using BIRT to extract the report. How can I get all the timespent values from taskA,B,C and D and put that in a report?

Thanks
Dhanya