A differential U$-$manometer is connected at the two point A and B of two pipes at different level such that $A$ is at higher level than $B.$ The pipe A contains liquid of Specific gravity$=1\mathrm{.}5$ while pipe B contain a liquid of Specific gravity $0\mathrm{.}9.$ The pressure at A and $B$ are $1kg\frac{f}{c}{m}^2$ and $1\mathrm{.}8kg\frac{f}{c}{m}^2.$ Find the difference in mercury level in differential manometer. The difference in the level between point A & B is $3m,$ where as the difference in the level of point of interface of mercury with liquid in left limb to the point B is $2\mathrm{.}0m.($density of mercury is $13600k\frac{g}{m^3}.)$