Answer:
9
Step-by-step explanation:
Radius = x
The triangle in the given image is a right angled triangle.
By Pythagoras theorem,
x² + 12² = ( x + 6 )²
x² + 144 = x² + 36 + 12x
x² - x² = 36 - 144 + 12x
0 = - 108 + 12x
12x = 108
x = 108 / 12
x = 9
