A dog instantly spots a squirrel sitting on the ground 15m away. She approaches the squirrel at a constant rate of 2m/s and the squirrel darts straight up the tree at a constant rate of 4m/s. Assuming the ground is smooth and flat and the tree is perfectly vertical:

a) At what rate is the distance between the dog and the squirrel changing at the moment when they are the closest together? (i.e. at the minimum distance apart?)

b) Determin the time at which the distance is at its minimum

c) Calculate the minimum distance between the dog and the squirrel.

I know that this problem involves the dog and squirrel forming a triangle, but there doesnt seem to be enough information given to solve the question, please help.