using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        List<int> grades = new List<int>() {99,85, 70, 65, 55};

        foreach (var item in grades)

        {

            var (grade, remarks) = item.GetGradeWithRemarks();

            Console.WriteLine($"{item, -3}{grade,-3}{remarks}");

        }

    }

}

public static class Extensions

{

    public static (string grade, string remarks) GetGradeWithRemarks(this int score) => score switch

    {

        >= 90 =>          ("A", "Great job"),

        >= 80 and < 90 => ("B", "Good"),

        >= 70 and < 80 => ("C", "Okay"),

        >= 60 and < 70 => ("D", "Better study"),

        >= 50 and < 60 => ("F", "You failed"),

        _ => throw new ArgumentOutOfRangeException(

            nameof(score), score, "Unexpected value")

    };

​

}