Mr. Donald Duck went to the concert and drove at a speed of 24 kilometers per hour. It took him three hours to arrive. After driving for half an hour, he found that he forgot to bring his admission ticket. The whole journey is 24× 3 = 72km, and it takes 0.5×2 = 1 hour from departure to return home.

Then when he starts from home again, the time left for him is only 3- 1 = 2 hours.

So he will arrive on time at the speed of 72÷2 = 36km = 36000m m per hour.