SPEED of boat in still water : Speed of STREAM = 5 : 1Downstream speed = 24 kmphFormula used:Distance/time = speedDownstream speed = Speed of boat in still water + Speed of streamUpstream speed = Speed of boat in still water – Speed of streamCalculation:LET the speed of the boat in still water and speed of the stream be 5x and x respectivelyAccording to the question,5x + x = 24X = 4Upstream speed = 5x – x = 16 kmph∴ Required time = 48/16 = 3 hours