Mr. Smith needs to travel a distance of 150 miles for a business trip. He plans to drive a portion of the trip and then take a train for the remaining distance. He drives at a speed of 60 mph and the train travels at a speed of 100 mph. If the total travel time for the trip is 2 hours, how many miles does Mr. Smith drive before boarding the train? Let's think step by step and output the final answer within \boxed{}.
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