$(20$ points$)$

$1\mathrm{.}41$ Figure Pl$\mathrm{.}41$ shows a closed tank holding air and oil to which is connected a U$-$tube mercury manometer and a pressure gage. Determine the reading of the pressure gage, in $lb\frac{f}{i}{n}^2($gage$).$ The densities of the oil and mercury are $55$ and $845,$ respectively, each in $l\frac{b}{f}{t}^3.$ Let $g=32\mathrm{.}2f\frac{t}{s^2}.$

FIGURE P$1-41$