Problem: a boat can travel with a speed of 15 km / hr in still water . if the speed of the stream is 6 km / hr , find the time taken by the boat to go 86 km downstream .
Rationale: "speed of boat in still water = 15 km / hr speed of the stream = 6 km / hr speed downstream = ( 15 + 6 ) = 21 km / hr time taken to travel 86 km downstream = 86 â  „ 16 = 17 â  „ 4 = 4.1 hours answer is a"
annotated_formula: divide(86, add(15, 6))