计算列表字典中所有对象的总成本

我是 C# 的编程学生，我被要求编写一个应用程序，但我无法弄清楚如何获取所有对象并计算总价格。

如果您可以将我引用到另一个页面或答案，任何帮助都会很好

谢谢它public decimal TotalCost()

namespace GCUShows
{
    public class Booking
    {
        private const int LIMIT = 6;
        // TODO: This class should include the following:
        // instance variable show which is a reference to a Show object
        public Show show;
        private int bookingID;
        public List<ITicket> tickets;
        public int BookingID
        {
            get { return bookingID; }
            set { bookingID = value; }
        }
        public Booking(Show show)
        {
            this.BookingID = BookingIDSequence.Instance.NextID;
            this.show = show;
            show.AddBooking(this);
            this.tickets = new List<ITicket>();
        }
        public void AddTickets(int number, TicketType type, decimal fee)
        {
            // TODO:this method should instantiate the specified number of tickets of the
            // specified type and add these to the list of tickets in this booking
            if (type == TicketType.Adult)
            {
                for(int i =0; i < number; i++)
                {
                    tickets.Add(new AdultTicket(show.Title, fee));
                }
            }
                else if (type == TicketType.Child)
                {
                    for(int i=0; i< number; i++)
                    {
                        tickets.Add(new ChildTicket(show.Title));
                     }
                }
            else if (type == TicketType.Family)
            {
                for (int i = 0; i < number; i++)
                {
                    tickets.Add(new FamilyTicket(show.Title, fee));
                }
             }
        }
        public string PrintTickets()
        {
            string ticketInfo = "Booking " + bookingID.ToString() + "'n";
            foreach (ITicket ticket in tickets)
            {
                ticketInfo += ticket.Print();
            }
            return ticketInfo;
        }
        public decimal TotalCost()
        {
            // TODO: this method should return the total cost of the tickets in this booking
        }
        public override string ToString()
        {
            return string.Format("{0}: Total Cost={1:c}", bookingID, TotalCost());
        }
    }
}