The equation is (x-5)2+(y-3)2=r2, because the equation of a circle with centre at the x-y origin is x2+y2=r2 where r is the radius. So the equation is adjusted to make the origin (5,3) instead of (0,0). To find r, simply substitute x=-3 and y=9:
(-8)2+(6)2=r2, making r2=64+36=100 (r=10).
Equation is (x-5)2+(y-3)2=100