A boat goes 100 km downstream in 10 hours, and 60 km upstream in 15 hours. The speed of the stream is? Pick:  A) 3km/h  B) 4km/h  C) 6km/h  D) (1/2) km/h  E) E)None
100 --- 10 DS = 10   ? ---- 1   60 ---- 15 US = 4   ? ----- 1 S = (10 - 4)/2= 
<gadget id="calculator">(10 - 4)/2</gadget>
<output>3</output>
3 kmph   3km/hNSWER:3km/h
<result>A</result>
A boat goes 100 km downstream in 10 hours, and 60 km upstream in 15 hours. The speed of the stream is?