In the given figure chords AB and CD of a circle intersect at $P$. If $AB$ = 5 cm, $PB$ = 3cm and $PD$= 4cm, then find the length of $CD$.<BR>

Question

$\begin{array}{1 1} (a)\;2\; cm \\ (b)\; 4\; cm \\ (c)\; 6\;cm \\ (d)\; 8\;cm \end{array}$</span$