# Bottle falls during Boating $$\ddot \frown$$

A boat travels upstream in a river with a constant but unknown speed $$v$$ with respect to water. At the start of this trip upstream, a bottle is dropped over the side. After $$7.5~minutes$$ the boat turns around and heads downstream. It catches up the bottle when the bottle has drifted $$1~km$$ downstream from the point at which it was dropped into the water. Then the velocity of water current is (in $$km/hr$$)

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