Let speed of boat in still water = $$x$$ km/h and speed of stream = $$y$$ km/h => Upstream speed of boat = $$(x-y)$$ km/h Downstream speed = $$(x+y)$$ km/h Acc to ques : => $$frac{24}{x-y} + frac{28}{x+y} = 6$$ and $$frac{30}{x-y} + frac{21}{x+y} = 6frac{1}{2}$$ Solving above equations, we get : $$x$$ = 10 km/h and $$y$$ = 4 km/h