Provide your best answer for the following math problem. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The problem is: two spherical balls lie on the ground touching . if one of the balls has a radius of 4 cm , and the point of contact is 6 cm above the ground , what is the radius of the other ball ?
14 cm
2.4 cm.