A motorboat can go at 21 kmph and still water. It takes 7 hours to row from A to B and back. What is the distance between A and B if the speed of the stream is 3 kmph?  Options.
A) 65 km
B) 85 km
C) 55 km
D) 72 km
E) 40 km
Let the distance between A and B be x km.   Total time = x/(21 + 3) + x/(21 - 3) = 7   =&gt; x/24 + x/18 = 7 =&gt; (4x + 3x)/72 = 7 =&gt; x = 72 km.   ANSWER:72 km
<result>D</result>
A motorboat can go at 21 kmph and still water. It takes 7 hours to row from A to B and back. What is the distance between A and B if the speed of the stream is 3 kmph?