private void SelectionItemComboBox(object sender, SelectionChangedEventArgs e)
        {            
            string carBrands = comboCarBrands.Text;
            SecondWindow secondWindow = new SecondWindow(this);
            secondWindow.Show();
        }

        MainWindow main;
        public SecondWindow(MainWindow mainWindow)
        {
            InitializeComponent();
            main = mainWindow;
            // извлечение значения из comboBox-a марки автомобиля            
            tbx_carBrand.Text = main.comboCarBrands.Text;
        }