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
How many minutes would it take him to walk 20 miles alone? ** Alone it would take him 9*20=<<9*20=180>>180 minutes
How many minutes would it take him to walk 20 miles with his brother? ** With his brother, it would take him 12*20=<<12*20=240>>240 minutes
How many minutes longer would it take him to walk 20 miles if he had to take his brother? ** 240-180=<<240-180=60>>60 more minutes
#### 60