add days in date in gridview using radio buttons

protected void gvImages_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        SqlConnection con = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=D:\site\SamsungClassifieds\App_Data\Dorknozzle.mdf;Integrated Security=True;User Instance=True");
        con.Open();
        
        //DateTime date = DateTime.Now;
        //date = date.AddDays(30);
        //int userid = Convert.ToInt32(gvImages.DataKeys[e.RowIndex].Values["lbladid"].ToString());
        Label lbladid = (Label)gvImages.Rows[e.RowIndex].FindControl("lbladid");
        TextBox txttitle = (TextBox)gvImages.Rows[e.RowIndex].FindControl("txttitle");
        TextBox txtdesc = (TextBox)gvImages.Rows[e.RowIndex].FindControl("txtdesc");
        Label lblprice = (Label)gvImages.Rows[e.RowIndex].FindControl("lblprice");
        TextBox txtprice = (TextBox)gvImages.Rows[e.RowIndex].FindControl("txtprice");
        RadioButton rd1 = (RadioButton)gvImages.Rows[e.RowIndex].FindControl("rb30");
        RadioButton rd2 = (RadioButton)gvImages.Rows[e.RowIndex].FindControl("rb60");
        RadioButton rd3 = (RadioButton)gvImages.Rows[e.RowIndex].FindControl("rb90");
      
        
            SqlCommand cmd = new SqlCommand("UPDATE AD_DETAIL SET AD_TITLE ='" + txttitle.Text + "',AD_DESC ='" + txtdesc.Text + "',AD_PRICE ='" + txtprice.Text + "'WHERE AD_ID = '" + lbladid.Text + "'", con);
            
            cmd.ExecuteNonQuery();
            gvImages.EditIndex = -1;
            Binddata();
            con.Close();
        

    }