AB and CD are two parallel chords of a circle with center O Such that $AB= 6\;cm$ and $CD= 12\;cm$ . The Chords are on the same side of the centre and the distance between them is $3\;cm$ The radius of the circle is

Question

$\begin{array}{1 1} 6\;cm \\ 5 \sqrt 2\;cm \\ 7\;cm \\3 \sqrt{5}\;cm \end{array} $