Let speed of man upstream = $$x$$ km/h and speed of man downstream = $$y$$ km/h Acc to ques, => $$frac{24}{x} + frac{54}{y} = 6$$ => $$frac{4}{x} + frac{9}{y} = 1$$ -------------Eqn(1) and $$frac{36}{x} + frac{48}{y} = 8$$ => $$frac{9}{x} + frac{12}{y} = 2$$ -------------Eqn(2) Solving equations (1) & (2), we get : => $$x = frac{11}{2}$$ and $$y = 33$$ $$ herefore$$ Speed of man in still water = $$frac{1}{2}$$ (downstream + upstream) = $$frac{1}{2} (frac{11}{2} + 33)$$ = $$frac{77}{4} = 19.25$$ km/h