using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public class Book

    {

        public int Id {get; set;}

        public string Name {get; set;}

        public decimal Price {get; set;}

    }

    public static void Main()

    {

        List<Book> books = new()

        {

            new Book

            {

                Id = 1,

                Name = "AA",

                Price = 19.0000M

            },

            new Book

            {

                Id = 2,

                Name= "BB",

                Price = 18.0000M

            },

            new Book

            {

                Id = 3,

                Name = "CC",

                Price = 30.0000M

            },

            new Book

            {

                Id = 4,

                Name = "DD",

                Price = 9.0000M,

            },

        };

        List<(decimal Category, List<Book> Books)> groupedBooks = books

            .GroupBy(book => Math.Ceiling(book.Price / 10) * 10,

                (category, booksInCategory) => ( 

                    Category: category, 

                    Books: booksInCategory.ToList() ))

            .OrderBy(gr => gr.Category)

            .ToList();

        foreach (var gr in groupedBooks)

        {

            Console.WriteLine($"Category: {gr.Category}");

            foreach (var book in gr.Books)

            {

                Console.WriteLine($"\tBook: {{ Id: {book.Id}\tName: {book.Name}\tPrice: {book.Price} }}");

            }

            Console.WriteLine();

        }

    }

}