Explanation:

- Let's say the speed of the boat in still water is 4x and the speed of the current is 3x.

- Downstream speed (boat + current) is 4x + 3x = 7x.

- Upstream speed (boat - current) is 4x - 3x = x.

- Distance covered downstream is 126 km, and upstream also 126 km.

- Time taken downstream = Distance/Speed = 126/7x hours.

- Time taken upstream = 126/x hours.

- Total time for both directions is 48 hours.

- Therefore, 126/7x + 126/x = 48.

- Solving, we get 18x = 21, so x = 21/18.

- Speed of boat in still water = 4x = 4 * (21/18) = 14/3 = 4.67 km/hr.

Then simplifying gives 14 km/hr for x = 3, so the resolved form doesn't fit with common options.

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