A boat covers a certain distance downstream in 1 hour, while it comes back in 11⁄2 hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water? Choose the correct choice from the following.
A) 14 kmph
B) 15 kmph
C) 13 kmph
D) 12 kmph
E) None of these
Explanation :   Let the speed of the water in still water = x   Given that speed of the stream = 3 kmph   Speed downstream = (x+3) kmph   Speed upstream = (x-3) kmph   He travels a certain distance downstream in 1 hour and come back in 11⁄2 hour.   ie, distance travelled downstream in 1 hour = distance travelled upstream in 11⁄2 hour   since distance = speed × time, we have   (x+3) × 1 = (x−3)(3/2)   =&gt; 2(x + 3) = 3(x-3)   =&gt; 2x + 6 = 3x - 9   =&gt; x = 6+9= 
<gadget id="calculator">6+9</gadget>
<output>15</output>
15 kmph. Answer : Option 15 kmph
<result>B</result>
A boat covers a certain distance downstream in 1 hour, while it comes back in 11⁄2 hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?