 
<translate> Saurin jirgin ruwa a cikin ruwa mai nutsuwa = (60 + 100) / 2 = 80 kmph. Saurin rafin = (100-60) / 2 = 20 kmph Saboda haka, amsar ita ce (D). <eng> Speed of the boat in still water = (60+100)/2 = 80 kmph. Speed of the stream = (100-60)/2 = 20 kmph
Therefore, the answer is (D). 