The equation of a circle in the standard (x,y) plane is:

$$(x-h)^{2}+(y-k)^{2}=r^{2}$$

Where (h,k) is the center of the circle and r is the radius.

$$r^{2}=144$$ $$=> r=12$$

The circle intersects with the x-axis at (0,12), (-12,0)