Question 1201410
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(a) The effective downstream velocity is the sum        7 + 4 = 11 km/h  (relative to the banks of the river).


(c) The effective upstream   velocity is the difference 7 - 4 = 3 km/h  (relative to the banks of the river).
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Do the rest on your own.


To make illustrations / diagrams, use a pen (or a pencil) and a paper.