private void DeleteButton_Click(object sender, RoutedEventArgs e)
        {
            string     performanceName = performancesComboBox.SelectedValue.ToString();
            string     clientName      = clientsComboBox.SelectedValue.ToString();
            DateTime   date            = ConvertStringToDateTime(dateComboBox.SelectedValue.ToString());
            typeTicket type            = Cashbox.FindTicket(typeComboBox.SelectedValue.ToString());

            if (cashbox.ReturnTicket(performanceName, date, clientName, type))
            {
                msgTextBlock.Text = "Билет успешно сдан в кассу.";
            }
            else
            {
                msgTextBlock.Text = "Не найден данный билет, на указанный спектакль.";
            }
        }