Ritu can row downstream 20km in 2 hours, and upstream 4km in 2 hours. Find her speed of rowing in still water and the speed of the current.

In calm water, the speed of the river and the rower's speed are added downstream and removed upstream. Equations based on the supplied data might be created using this.

Let Ritu go at a speed of x km/hr in calm water and the current at y km/hr.

Then speed downstream $=(x+y)\mathrm{km}/\mathrm{hr}$ speed upstream $=(x-y)\mathrm{km}/\mathrm{hr}$
we know,  $Time=\frac{\text{ Distance }}{\text{ Speed }}$
Then $\frac{20}{x+y}=2$ and $\frac{4}{x-y}=2$
$\Rightarrow x+y=10\dots \left(1\right)$
$x-y=2\dots \left(2\right)$
combining both, we obtain, $2\mathrm{x}=12\Rightarrow \mathrm{x}=6$
Thus using (1) $y=10-6=4$
As a result, Ritu moves at a speed of $6 \mathrm{km}/\mathrm{hr}$ and the current's velocity is $4 \mathrm{km}/\mathrm{hr}$.

Hence, the correct answer is option A.