how to insert text automatically with the help of combo box

Private Sub cbo_mytrip_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles cbo_mytrip.SelectedIndexChanged
     If cbo_mytrip.SelectedValue = "--select driver name--" Then
         objdbconn.OpenConn()
         msSQL = " select b.vehicle_no from tae_mst_tdriver " & _
                 "left join tae_mst_tvehicle b on a.vehicle_gid=b.vehicle_gid" & _
                  "where driver_gid='" & cbo_mytrip.SelectedValue & "'"
         objODBCDataReader = objdbconn.GetDataReader(msSQL)
         If objODBCDataReader.HasRows = True Then
             txttrip_vehiclenoedit.Text = objODBCDataReader.Item("vehicle_gid").ToString
         End If
         objODBCDataReader.Close()
         objdbconn.CloseConn()
     End If
 End Sub