Both lines AB and CD are secant lines beacuse in two points they are touching the circunference. There is a Theorem which says the following
[tex]PB\cdot PA=PD\cdot PC[/tex]
Since the distance from the center of the circle to each secant line is the same (5 units), we could assume that the both secant lines are similar. saying:
[tex]PB=PD;\text{ }PA=PC\Rightarrow AB=CD[/tex]
Then the lenght of CD is:
[tex]CD=2\cdot EB=2(7)=14[/tex]
