A person covers certain distance in 8 hours at a speed of 6 km/h and some more distance in 10 hours at a speed of 4 km/h. Find his average speed for the entire distance covered.
5 \( \frac{8}{9} \) kmph
3 \( \frac{8}{9} \) kmph
4 \( \frac{8}{9} \) kmph
6 \( \frac{8}{9} \) kmph