Circle

If the circles $C_1: x^2+y^2+2 x+4 y-20=0$, $C_2: x^2+y^2+6 x-8 y+9=0$ have $n$ common tangents and the length of the tangent drawn from the centre of similitude to the circle $C_2$ is $l$, then $\frac{l}{n^2}=$