Answer:
R = 13 cm, x = 5 cm
Explanation:
We can see, that AO = BO = EO
First, we have to find AO from ∆OAD by using the Pythagorean theorem:




Now, let's write that EO = (8 + x)
Since AO = EO, we can write an equation:

Let's square the whole equation:




Let's divide both sides of the equation from -16:

OB = 8 + x = 8 + 5 = 13 (radius)