if a dog is sitting on a porch and 20 meters away a cat is playing. if the dog travels at 4m per second and the cat travels at 2m per second. how many seconds does the cat have before he should be up a tree

I assume they are traveling toward one another, rather than the dog chasing the cat.

20/(4+2) = ?

If the dog is chasing the cat,

20/(4-2) = ?

How far away is the tree?