A man swims downstream 60 km and upstream 36 km taking 6 hours each time. What is his speed in still water.

Let us assume speed of man in still water = x kmph

Speed of still water = y kmph

Swims  in downstream

$=\frac{60}{x+y}=6$

$x+y=10kmph$

Swims in upstream

$=\frac{36}{x-y}=6$

$x-y=6kmph$

$From\left(i\right)\&\left(ii\right)$

$2x=16$$\Rightarrow x=8kmph$

Man's speed in still water $x=8kmph$