Problem $3$: A large tank containing mostly water is held under pressure, with the pressure

measured via a manometer with several fluids. Find the gauge pressure of the air inside the tank

given the densities of the fluids: ${}_{H_{2}O}=1000k\frac{g}{m^3},{}_{\text{o}\text{i}\text{l}}=0\mathrm{.}850{}_{H_{2}O},$ and ${}_{H_g}=13\mathrm{.}6{}_{H_{2}O}.$

Take the heights to be $h_1=0\mathrm{.}7m,h_2=0\mathrm{.}6m,$ and $h_3=0\mathrm{.}8m.$