John drives from City A to City B, which is 150 miles away. On his return trip, he takes a different route that is 10 miles longer but drives 5 miles per hour slower than he did on his way to City B. If the total driving time for the round trip is 7 hours, what was John's driving speed on the way to City B? Let's think step by step and output the final answer within \boxed{}.
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