2. Master Zhang drove the truck from the county to the provincial capital, unloaded the goods immediately after arriving at the provincial capital, and immediately returned along the road. When he was driving, the speed was 64 kilometers per hour. When he came back, the speed was 56 kilometers per hour, and it took 12 hour for a round trip (ignoring the time of unloading in the provincial capital). How many kilometers did Master Zhang walk from the provincial capital to the county seat?

3.(400/x - 5)(x+4)-400=400+9x

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