20. In the figure below, $A B C$ is a triangle with $A B=10 \mathrm{~cm}$ and $B C=40 \mathrm{~cm}$. Points $D$ and $E$ lie on side $A C$ and point $F$ on side $B C$ such that $E F$ is parallel to $A B$ and $D F$ is parallel to $E B$. Given that $B E$ is an angle bisector of $\angle A B C$ and that $A D=13.5 \mathrm{~cm}$, fmd the length of $C D$ in $\mathrm{cm}$.