A gas sample is attached to an open$-$ended mercury manometer, as shown below. The difference in heights of the mercury in the manometer is $15\mathrm{.}9cm$ when the atmospheric pressure is $735$ torr. Given that the density of mercury is $13\mathrm{.}6\frac{g}{m}L,$ the pressure of the enclosed gas is

$x$ atm.

Write your answer as $0\mathrm{.}123$atm $(3$ significant figures$)$

The correct answer is: $0\mathrm{.}758$atm

$?$