Let speed of boat = $$x$$ km/hr and speed of stream = $$y$$ km/hr Thus, downstream speed = $$(x+y)$$ km/hr and upstream speed = $$(x-y)$$ km/hr Using, time = distance/speed => $$(frac{60}{x+y})+(frac{20}{x-y})=4$$ => $$frac{15}{x+y}+frac{5}{x-y}=1$$ ---------------(i) Similarly, $$(frac{40}{x+y})+(frac{40}{x-y})=6$$ => $$frac{1}{x+y}+frac{1}{x-y}=frac{3}{20}$$ ------------(ii) Solving equations (i) and (ii), we get : $$x=24$$ and $$y=16$$ $$ herefore$$ Speed of stream = 16 km/hr => Ans - (B)