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? Let's think first. Chain of thought:
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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.
Therefore, the answer is 60.
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