Problem #WSP-000198

Problem

Let $CB$ and $CD$ be tangents to the circle with the centre $A$, let $E$ be the point of intersection of the line $AC$ with the circle. Draw $FG$ as the segment of a tangent drawn through the point $E$ between the lines $CB$ and $CD$. Find $FG$ if the radius of the circle is $15$ and $AC=39$.