$06.$ For a cylindrical parabolic concentrator of $2\mathrm{.}5$m width and $9$m lemgth, the outside diameter of the absorber tube is $6\mathrm{.}5$ cm$.$ Find the CR of the collector Ops: A$.11\mathrm{.}93$ B$.10\mathrm{.}56.07\mathrm{.}43$ D$.13\mathrm{.}78$