A mercury $($specific gravity $=13\mathrm{.}6)$ manometer connected across an orificemeter fitted in a pipe shows a manometer reading of $2$ cms$.$ If the manometer liquid is changed to carbon tetrachloride $($specific gravity $=1\mathrm{.}6),$ then for the same flow rate of water the new manometer reading will be $\_\_\_\_\_\_\_\_\_$ cms$.$

$17$

$42$

$84$

$1\mathrm{.}8$