In vb.net ,how to sum column values and put it in a textbox of same page

Question

Hi all,

   Iam using vb.net and WPF
   In a wpf window im showing a datagrid in the load event
   while in the load event itself,i need to count grand total
   amount from a single datagrid column and add it to a
   textbox in same page .

   My page looks like this

  MY DATAGRID

   Item              Quantity       Total
   ``````        ````````       `````
   Shirt                    2              200
   Pant                    1              500
   Tie                       -                -
   Belt                     2              100

 
 MY TEXTBOX   --->  Grand Total amount : -    800


  How do i do tat if iam counting from a ((Total Column )) DTG
  and adding it and showing it in my (( GRAND TOTAL AMOUNT)) TEXTBOX

  Thanks in advance

  Naveen.....