In an event, A rows his boat upstream in a river flowing with a steady speed of 6 km/hr and then returns to the same point without rowing (i.e. only with the speed of river). If the total distance covered by A is 42 km and the time taken in rowing the boat upstream is 4 hours more than his return journey, find the speed of A in still water.

Let the speed of A in still water be x km/hr. The upstream speed is (x - 6) km/hr, and since the total distance covered is 42 km, the one-way distance is 21 km, making the return time 21 divided by 6, which is 3.5 hours. The upstream time is 4 hours more than the return journey, so it equals 7.5 hours. Using the Time, Speed and Distance formula, 21 divided by (x - 6) equals 7.5, which solves to x = 8.8 km/hr.

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