4 Circles of Pi Day

Two circles $O_1 , O_2$ are tangent to each other at point $A$ and has a common tangent $L_1$ at points $B , C$ . Another line $L_2$ is parellel to line $L_1$ and tangent to circle $O_1$ . If $O_1$ has a radius of 9, $O_2$ has a radius of 4, $O_3$ is tangent to $O_1 , O_2$ and $L_1$ , $O_4$ is tangent to $O_1 , O_2$ and $L_2$ , find the geometric mean of the radiuses of the 4 circles.