A boat crossed a lake from North to South at the speed of 4 km/h, entered a river and covered twice as much distance going upstream at 3 km/h. It then turned around and stopped at the south shore of the lake. If it averaged 4 km/h that day, what was its approximate downstream speed?	Choose the correct choice from the following answers:
A) 4 B) 5 C) 6 D) 7 E) 8
Another way will be:   Total time for the trip = distance covered in Lake/speed in still water +distance covered upstream/upstream speed + distance covered downstream/downstream speed   If 5D is the total distance, then distance covered in lake = D, distance covered upstream = 2D and distance covered downstream = 2D   =&gt;5D/4 = D/4 + 2D/3 + 2D/x (where x is the downstream speed)   =&gt; 5/4 = 1/4 + 2/3 +2/x (div. both sides by D)   =&gt; 1.25 = .25+.66 +.33/x =&gt; x=5.99 ~6   option 6
<result>C</result>
A boat crossed a lake from North to South at the speed of 4 km/h, entered a river and covered twice as much distance going upstream at 3 km/h. It then turned around and stopped at the south shore of the lake. If it averaged 4 km/h that day, what was its approximate downstream speed?