A boat crossed a lake from North to West at the speed of 5 km/h, entered a river and covered twice as much distance going upstream at 4 km/h. It then turned around and stopped at the south shore of the lake. If it averaged 3.6 km/h that day, what was its approximate downstream speed?	Choose the correct choice from the following options:
A) 2  B) 3  C) 6  D) 7  E) 8
One way of solving this is:   Speed of boat on still water (lake)=5kmph   Speed upstream = 4kmph = speed in still water - speed of river =&gt; speed of river = 1kmph   =&gt;Speed downstream = speed in still water + speed of river = 5+1= 
<gadget id="calculator">5+1</gadget>
<output>6</output>
6kmph   Ans is 6
<result>C</result>
A boat crossed a lake from North to West at the speed of 5 km/h, entered a river and covered twice as much distance going upstream at 4 km/h. It then turned around and stopped at the south shore of the lake. If it averaged 3.6 km/h that day, what was its approximate downstream speed?