Problem $1$: Determine the pressure at $A$ if the gauge pressure at $B$ is $87$ kPa $.$ The specific weights $($weight per unit volume$)$ of each fluid are ${}_{\text{w}\text{a}\text{t}\text{e}\text{r}}=9790\frac{N}{m^3},{}_{\text{m}\text{e}\text{r}\text{c}\text{u}\text{r}\text{y}}=133100\frac{N}{m^3},{}_{\text{o}\text{i}\text{l}}=8720\frac{N}{m^3}.$