Question 14
In the adjoining figure, points $B$ and $C$ lie on line segment $AD,$ and $AB,$ $BC,$ and $CD$ are diameters of circles $O,$ $N,$ and $P,$ respectively. Circles $O,$ $N,$ and $P$ all have radius $15,$ and the line $AG$ is tangent to circle $P$ at $G.$ If $AG$ intersects circle $N$ at points $E$ and $F,$ then chord $EF$ has length
