If you'd draw the circle, making it tangent to the y-axis,
and with center (3,-1), you'd easily be able to find the radius,
and then you'd know that C would be the square of the radius.



Now draw in the radius from the center (3,-1) over to the y-axis 
where it's tangent:



You can easily tell that radius is 3 units long, so r=3

So the equation:



is





So now you know that A=3, B=-1 and C=9.

Edwin