Explanation:

- The man first walks 5 km in a certain direction.

- Next, he walks south for 4 km.

- He ends up in an eastward position relative to the starting point.

To find the distance from the starting position:

- He forms a right-angled triangle with:

- Adjacent side (horizontal component): 5 km (east)

- Opposite side (vertical component): 4 km (south)

- Use the Pythagorean theorem $a^2+b^2=c^2$:

- $c=\sqrt{5^2+4^2}$

- $c=\sqrt{25+16}$

- $c=\sqrt{41}$

- $c\approx 6.4$ km

Options summary:

- None of the listed options match $\approx 6.4$ km.

- Hence, no correct option.