how to calculate percenatge on total column and display it in datagridview in vb.net

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="true" OnRowDataBound="CustomersGridView_RowDataBound">
 </asp:GridView>

DataTable dt = new DataTable();
    protected void Page_Load(object sender, EventArgs e)
    {
        dt.Columns.Add("amt", typeof(Int32));
        dt.Columns.Add("pamt", typeof(Int32));
        dt.Columns.Add("damt", typeof(Int32));
        DataRow dr=dt.NewRow();
        dr[0] = 200;
        dt.Rows.Add(dr);
        DataRow dr1 = dt.NewRow();
        dr1[0] = 400;
        dt.Rows.Add(dr1);
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
   protected void CustomersGridView_RowDataBound(Object sender, GridViewRowEventArgs e)
    {

        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            // Display the company name in italics.
            e.Row.Cells[1].Text =Convert.ToString(Convert.ToInt32(e.Row.Cells[0].Text)*15/100);
            e.Row.Cells[2].Text = Convert.ToString(Convert.ToInt32(e.Row.Cells[1].Text) * 15);
        }

    }