IPrinter and PrinterService modified.cs

    // this in Services\ConsolePrinter\IPrinter
    public interface IPrinter
    {
        void PrintToConsole(int Result);
        
        // this was added
        void PingPong();
    }
    
    // this in Services\ConsolePrinter\PrinterService
        public class PrinterService : IPrinter
    {
        public PrinterService() 
        {
            System.Console.WriteLine("I am a new PrinterService");
        }

        public void PrintToConsole(int Result)
        {
            System.Console.WriteLine("Result = "+Result);
        }
        
        // this was added
        public void PingPong() 
        {
            System.Console.WriteLine("Ping Pong");
        }
    }