Huntsman and dog

Due to the fact that we do not know exactly how fast the dog is running, we compare his velocity to the velocity of the huntsman. What distance will the dog cover, if he is running three times faster than the huntsman, for example?

Answer: The dog will cover a distance of...

a)... 5 km, because the huntsman is coming a little bit closer and closer to the dog on the way to the hunting lodge.

b)... 6 km, because the dog covers a three times larger distance because of the three times higher velocity during the same period of time.

c)...9 km, because the dog also needs three times longer than the huntsman if the dog is running three times faster than the huntsman.

c)...12 km, because the dog can cover three times the distance of the outward and return during the same period of time as the huntsman because of the three times higher velocity.