In the figure a circle with center O is inscribed in a quadrilateral ABCD such that, it touches BC,AB,AD and CD at points P,Q,R and S respectively . If $AB=29\;cm, AD= 23\;cm, \angle B=90^{\circ}$ and $DS=5 \;cm$ then the radius of the circle is

Question

$\begin{array}{1 1} 11\;cm \\ 18\;cm \\6\;cm \\15\;cm \end{array} $