public static void Start() { //Create an instance of the GSM class. var myPhone = new GSM("GalaxyS6", "Samsung"); //Add few calls. myPhone.AddCall(new Call(new DateTime(2015, 3, 5, 9, 30, 10), "0883448036", 140)); myPhone.AddCall(new Call(new DateTime(2015, 3, 4, 10, 12, 53), "0883428135", 230)); myPhone.AddCall(new Call(new DateTime(2015, 3, 12, 19, 3, 32), "0883451438", 423)); //Print call information myPhone.PrintCallHistory(); Console.WriteLine(); //Print the total price of the calls in the history for 0.37 per minute Console.WriteLine("Total calls price: ${0:0.##}", myPhone.GetCallsTotalPrise(0.37M)); //Remove the longest call from the history and calculate the total price again var longestCall = myPhone.CallHistory.OrderByDescending(x => x.Duration).First(); myPhone.DeleteCall(longestCall); Console.WriteLine("Longest call removed!"); Console.WriteLine("Total calls price: ${0:0.##}", myPhone.GetCallsTotalPrise(0.37M)); Console.WriteLine(); myPhone.PrintCallHistory(); //Finally clear the call history and print it. myPhone.ClearHistory(); Console.WriteLine("History cleared!"); myPhone.PrintCallHistory(); }