please help !! thanks in advance :D

[tex]CIRCLES[/tex]

◆ A little manipulation of the diagram
( as shown in the attachment ) 

Once you're done with this simple manipulation and the labeling, we get the equation : OB² + BC² = OC²

 • r² = ( r - 9 )² + 15² 

Solve this trivial equation to get : r = 17 

 • Radius = 17 is your final answer .
_____________________________________________________________

Hope this helps you :)