Joseph is travelling upstream by a boat with a speed of 30 kmph. If the speed of the current is 3 kmph, what is the total time required to reach a point 90 km away from the starting point and come back to the starting point?

The boat's speed in still water is 33 kmph, calculated by adding the upstream speed of 30 kmph and the current speed of 3 kmph. The downstream speed is 36 kmph, found by adding 33 and 3. The total time is 90 divided by 30 plus 90 divided by 36, which equals 3 hours plus 2.5 hours, resulting in 5 hours and 30 minutes.

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