using System;

using System.Collections.Generic;

using System.Linq;

​

public class Order

{

    public List<Items> items;

}

​

public class Items

{

    public String description;

    public int qty;

}

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        List<Items> temp = new List<Items>();

        Items item1 = new Items();

        item1.description = "item1";

        item1.qty = 3;

        temp.Add(item1);

        Items item2 = new Items();

        item2.description = "item2";

        item2.qty = 1;

        temp.Add(item2);

        List<Order> listOfOrders = new List<Order>();

        Order order = new Order();

        order.items = temp;

        listOfOrders.Add(order);

        //Console.WriteLine("results are " + temp.Sum(o=>o.qty));

        var results = listOfOrders.SelectMany(o => o.items).Sum(o => o.qty);

        Console.WriteLine("results are " + results );

    }

}