A man goes downstream on a boat to some destination and returns upstream to his starting place in 4.5 hours. If the speed of the boat in still water and the speed of the stream are 9 km/h and 5 km/h, respectively, then what is the distance of the destination from the starting place?

Using the boat and stream formula, the downstream speed is 9 + 5 = 14 km/h and the upstream speed is 9 - 5 = 4 km/h. Let the distance be x, so the total time is x/14 + x/4 = 4.5 hours. Solving the equation (2x + 7x)/28 = 4.5 gives 9x/28 = 4.5, which means x = 14. The distance of the destination from the starting place is 14 km.

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