A river flows with a uniform velocity vr. A person in a motorboat travels 1.13 km upstream, at which time she passes a log floating by. Always with the same engine throttle setting, the boater continues to travel upstream for another 1.42 km, which takes her 62.2 min. She then turns the boat around and returns downstream to her starting point, which she reaches at the same time as the same log does. How much time does the boater spend traveling back downstream?

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