John commutes to work every day. He drives to the train station, takes a train, and then walks to his office. His driving speed is 30 mph, the train speed is 60 mph, and his walking speed is 4 mph. If he spends 20 minutes driving, 1 hour on the train, and 15 minutes walking, what is the average speed for his entire commute? Let's think step by step and output the final answer within \boxed{}.
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