hey! The formula for the equation of a circle is r^2= (x-h)^2 + (y-k)^2
r= the radius (in your case you have the diameter so you do not need to square it)
(h,k)= is the center coordinates, so your center coordinate would be (4, -9). You now have your h (h=4) and your k (k=-9) so you can plug it in the formula! :)
