class User // пользователь
{
	 public int Id { get; set; }
	 public string Name { get; set; }
}

class Teen //подросток
{
	 public int UserId { get; set; }
	 public int Vozrast { get; set; }
}

void Main()
{
	List<User> users = new List<User>();
	users.Add(new User(){Id = 1, Name = "Саша"});
	users.Add(new User(){Id = 5, Name = "Петя"});
	users.Add(new User(){Id = 2, Name = "Оля"});
	users.Add(new User(){Id = 3, Name = "Миша"});
	users.Add(new User(){Id = 7, Name = "Коля"});
	users.Add(new User(){Id = 4, Name = "Наташа"});
	users.Add(new User(){Id = 6, Name = "Вася"});
	users.Add(new User(){Id = 8, Name = "Лора"});

	List<Teen> teens= new List<Teen>();
	
	teens.Add(new Teen(){UserId = 3, Vozrast = 10});
	teens.Add(new Teen(){UserId = 5, Vozrast = 12});
	teens.Add(new Teen(){UserId = 6, Vozrast = 15});
	
	
	users.Where(usr => teens.Any(t => t.UserId == usr.Id)).Dump();
	(users.Join(teens, usr => usr.Id, teen => teen.UserId, (usr, teen) => new {teen.UserId, usr.Name, teen.Vozrast})).Dump();

}