If $y+3x=0$ is the equation of a chord of the circle, $x^2+y^2-30=0$, then the equation of the circle with this chord as diameter is :

Question

$\begin{array}{1 1} x^2+y^2+3x+9y=0 \\ x^2+y^2-3x+9y=0 \\ x^2+y^2-3x-9y=0 \\ x^2+y^2+3x-9y=0 \end{array}$