public static void Opgave41()
        {
            while (true)
            {
                Monitor.Enter(lockThis);
                try
                {
                    tal += 2;
                    Console.WriteLine(tal);
                    Thread.Sleep(1000);
                }
                finally
                {
                    Monitor.Exit(lockThis);
                }


            }
        }

        public static void Opgave42()
        {
            while (true)
            {
                Monitor.Enter(lockThis);
                try
                {
                    tal--;
                    Console.WriteLine(tal);
                    Thread.Sleep(1000);
                }
                finally
                {
                    Monitor.Exit(lockThis);
                }
            }
        }