using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        // Create customers and orders

        var customers = new List<Customer>()

        {

            new Customer { Name="Raju", Orders = new [] {

                new Order { Id = 3443, Total = 14.56M },

                new Order { Id = 8642, Total = 20.87M }

            } },

            new Customer { Name="Roxana", Orders = new [] {

                new Order { Id = 9831, Total = 54.00M },

                new Order { Id = 10456, Total = 15.70M },

                new Order { Id = 12654, Total = 95.47M }

            } },

            new Customer { Name="Ali", Orders = new [] {

                new Order { Id = 523, Total = 5.87M },

            } },

        };

​

        var projection = customers

            .SelectMany(c => c.Orders)

            .Where(o => o.Total > 20M)

            .Select(o => o.Id);

​

        foreach (var orderId in projection)

        {

            Console.WriteLine(orderId);

        }

    }

​

    public static decimal SumOfOrderTotals(IEnumerable<Customer> customers)

    {

        return 0; // Return the sum of all order totals

    }

​

    public static Customer CustomerWithGreatestOrderTotal(IEnumerable<Customer> customers)

    {

        return null; // Return the customer with greatest order total

    }

​

    public static IEnumerable<Order> ThreeOrdersWithGreatestTotalsDescending(IEnumerable<Customer> customers)

    {

        return null; // Return the top three orders with greatest totals in a descending order

    }

}

​

public class Order

{

    public int Id { get; set; }

    public decimal Total { get; set; }

}

​

public class Customer

{

    public string Name { get; set; }

    public IEnumerable<Order> Orders { get; set; }

}