###Human: It takes Derek 9 minutes to walk a mile if he doesn't have to walk with his brother. If he has to take his brother it takes 12 minutes to walk a mile. How many minutes longer would it take him to walk 20 miles if he had to take his brother?, ### Assistant: Alone it would take him 9*20=180 minutes
With his brother, it would take him 12*20=240 minutes
240-180=60 more minutes 
 So the answer is :  60