The number of common tangents of the circles $x^2+y^2-4=0$ and $x^2+y^2-6 x-8 y-24=0$ is

If the equation of the circle whose radius is $\sqrt{10}$ and which touches the circle $x^2+y^2+2 x+8 y-23=0$ externally at the point $(1,2)$ is $x^2+y^2+a x+b y+c=0$, then $|a+b+c|=$

If a circle ' $S$ ' passing through the origin and having its centre on the line $x-y=0$ cuts the circle $x^2+y^2-4 x-6 y+10=0$ orthogonally, then the diameter of ' $S$ ' is

The equation of the circle passing through the points of intersection of the circles $x^2+y^2+6 x+4 y-12=0$, $x^2+y^2-4 x-6 y-12=0$ and having radius $\sqrt{13}$ is