Terelik GridView Control using Vb.Net

Hi All,
 
I am using Terelik Gridview control and able to get data. As my requirement is get value and Sum the value from "GridAggregateFunction.Sum" property. Then after I need to get the percentage in new column. Please let me know, how to added the new column to already existing Gridview and then how to get the percentage value to newly added column.
 
Example : Total: 1200 Percentage:480 <- (1200 *0.40)
 
I am using VB.net.
 
Please help me.
 
Thanks in Advance.