A girl can swim with speed `5 kmh ^(-1)` in still water. She crosses a river `2 km` wide, where the river flows steadily at `2 kmh^(-1)` and she makes strokes normal to the river current. Find how far down the river she go when she reaches the other bank.
Options:
(a) `1 km`
(b) `2km`
(c) `800m`
(d) `750m`