A differential manometer is connected at the two points A and B of two pipes as shown in figure. The pipe A contains a liquid of specific gravity $=1\mathrm{.}5$ while pipe $B$ contains a liquid of specific gravity$=0\mathrm{.}9.$ The pressure at A and B are $1kg\frac{f}{c}{m}^2$ and $1\mathrm{.}80kg\frac{f}{c}{m}^2,$ respectively. Find the difference in mercury level in the differential manometer.