Sarah is planning a road trip from City A to City B, which is 240 miles away. She drives the first 2 hours at a speed of 60 miles per hour. She then realizes that she needs to cover the remaining distance in the next 2 hours to reach her destination on time. What average speed does she need to maintain for the remaining part of her trip to arrive on time? Let's think step by step and output the final answer within \boxed{}.
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