Calvin went cycling in San Francisco, which is extremely hilly. He can pedal up a hill at a speed of 12 mph, and down a hill at a speed of 36 mph. If he went up and down a hill (back to the same point), what is his average speed (in mph) for the entire journey?

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A grocer has a stack of apples and a stack of oranges. After arranging them in neat rows, he realizes that he has 4 apples for every 3 oranges. Given that he has 168 apples, how many oranges does he have?

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