Perplexing Mensuration Question - sphere in a cone

Hello everyone.

This maths question is somewhat beyond my ken. One part of it talks about similarity while the other talks about mensuration. Still, I could not find an interrelationship between the clues given.

http://www.flickr.com/photos/47564170@N03/5025568684/ The image is at Mensuration Question | Flickr

What I know intuitively is that there is a Pythagoras' Theorem involved in finding the radius of the sphere. However, VD, which is 8cm, is solely a part of the hypotenuse. If I have the value of the hypotenuse, then I can use the Pythagoras' Theorem to find the radius of the cone.

Also, since triangle VDO is similar to triangle VCA, then it would be , and .

Can anyone give me hints? Help is greatly appreciated!