First, we can find that the kitten runs 4 meters per second because 2/3 of 6 is 4
Now we can find how far the puppy will go in 15 seconds
If he goes 6 meters in one second, we do 6*15 to get 90 meters
If the kitten goes 4 meters in one second, we do 4*15 to get 60 meters
So to find the distance between them we do 60+90 to get 150 meters