Alone it would take him 9*20=<<9*20=180>>180 minutes

With his brother, it would take him 12*20=<<12*20=240>>240 minutes

240-180=<<240-180=60>>60 more minutes

# Answer

60
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
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?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
60
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?
train