How to add Summary row at the bottom of grid in silvelight 4

See more:

C#

XAML

Silverlight

DataGrid

I have been working on DataGrid of Silverlight 4.

I needed to add few features to my grid like column search etc.

the last feature i wanted to add is, Summary row at the bottom.

I want summary row which will have facility to show summary of column selected by user.

For example, if there are 5 columns in grid and user wants to display summary of only 3 of them.
Summary of those 3 columns will be displayed and not of other two.

Problem:
I am not able to add summary row. Infact I dont have any direction for adding that kind of row into the datagrid.

I searched on internet, but most of the articles were not helpful to me.

So, here I am trying to find some direction or some direct solution for adding summary row at the bottom of grid.