$\begin{array}{1 1} (a)\; x^2+y^2-8x-12y+16=0 \\ (b)\; x^2+y^2+8x+12y+16=0 \\ (c)\; (x+4)^2 + (y+6)^2=36 \\ (d)\; \text{none of the above} \end{array}$