 
<translate> Ọsọ ụgbọ mmiri na-agba n'ime mmiri = (60+100) / 2 = 80 kmph. Ọsọ nke iyi = (100-60) / 2 = 20 kmph N'ihi ya, azịza ya bụ (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). 