Question 436021
<pre><font face = "consolas" color = "indigo" size = 4><b>
{{{drawing(400,400,-16,16,-16,16, 

circle(0,0,15), line(-12,9,12,9), line(0,0,0,9), 
locate(-6,9,12cm), locate(6,9,12cm),locate(0.3,4.5,9cm)

)}}}

We draw in a radius (in green), label its length R cm:

{{{drawing(400,400,-16,16,-16,16, 
green(line(0,0,-12,9)), locate(-7,4,Rcm),
circle(0,0,15), line(-12,9,12,9), line(0,0,0,9), 
locate(-6,9,12cm), locate(6,9,12cm),locate(0.3,4.5,9cm)

)}}}


That's a right triangle and we only need to find its
green hypotenuse R cm which is a radius of the circle.
We just use the Pythagorean theorem:

R² = 9² + 12²

R² = 81 + 144

R² = 225
      ___
 R = <font face = "symbol">Ö</font>225

 R = 15

So the radius is 15 cm.

Edwin</pre>