using System;

using System.Linq;

class Row {

    public DateTime Date { get; set; }

    public decimal Amount { get; set; }

    public decimal Balance { get; set; }

    public string Memo { get; set; }

}

​

class RateRange {

    public decimal? Min { get; set; }

    public decimal? Max { get; set; }

    public decimal Rate { get; set; }

}

​

​

public class Program

{

    public static void Main()

    {

        var rates = new [] {

            new RateRange { Min = null, Max = 1000, Rate = 0.1m },

            new RateRange { Min = 1001, Max = 2000, Rate = 0.2m },

            new RateRange { Min = 2001, Max = 4000, Rate = 0.3m },

            new RateRange { Min = 4001, Max = 10000, Rate = 0.4m },

            new RateRange { Min = 10001, Max = null, Rate = 0.4m },

        };

        var entries = new [] {

            new Row { Date = new DateTime(2023,1,1), Amount = 1200, Balance = 1200, Memo = "Transaction 1" },   

            new Row { Date = new DateTime(2023,1,15), Amount = 3200, Balance = 4400, Memo = "Transaction 2" },

            new Row { Date = new DateTime(2023,2,1), Amount = -1200, Balance = 3200, Memo = "Transaction 3" },

            new Row { Date = new DateTime(2023,2,15), Amount = 5000, Balance = 8200, Memo = "Transaction 4" },

            new Row { Date = new DateTime(2023,2,1), Amount = 4000, Balance = 12200, Memo = "Transaction 5" },

            new Row { Date = new DateTime(2023,2,15), Amount = 5000, Balance = 17200, Memo = "Transaction 6" },

        };

        var rows = from currentRow in entries

                   let nextRow = entries.Where(e => e.Date > currentRow.Date).OrderBy(e => e.Date).FirstOrDefault()

                   select new {

                        Date = currentRow.Date,

                        Amount = currentRow.Amount,

                        Balance = currentRow.Balance,

                        NextDate = nextRow == null ? (DateTime?)null : nextRow.Date

        };

        foreach (var r in rows) {

            Console.WriteLine($"{r.Date:dd/MM/yyyy} - {r.Balance:c0} - {((r.NextDate ?? DateTime.Today) - r.Date).TotalDays} days");    

        }

    }

}