SSRS: Need to find the total of specific type of data to another field

I have to create a SSRS report like below:

Name------Members-----Total
-----------------------------------

Project1.................................9
......Group1..........4
.......Group2.........5
Project2.................................5
......Group1.........5
Project3.................................10
......Group1..........3
......Group2..........2
......Group3..........5

(given....for alignment)

The group information varies depends on the project. I need to find the total of these group information to field total.

It would be great if any of any of you can help me on this.

Thanks,

Julie