Find the coordinates of the center and the radius of the circle given by the equation $\displaystyle y(y-4)+x(x+3)=0$

I know $\displaystyle (h,k)$ is the center which if I am right its $\displaystyle (4,-3)$ but how do I find the radius ?

if I take $\displaystyle y(y-4)+x(x+3)=0$ and expand it out to $\displaystyle y^2-4y+x^2+3x=0$ how do I enter that into $\displaystyle (x-h)^2+(y-k)^2=r^2$ Because I think I need to find atleast one coordinate to find my radius?