PROBLEM $3\mathrm{.}21$:

Gate $AB$ with a width of $1\mathrm{.}2m$ perpendicular to the page is shown in the figure.

The gate is hinged at point $A.$ The pressure read from the manometer on the left

is $-15k\frac{N}{m^2}.$ In the given system, calculate the force required to be applied to

point $B$ to keep gate $AB$ in equilibrium.

$($Specific weight of water and oil: ${}_{\text{w}\text{a}\text{t}\text{e}\text{r}}=9810\frac{N}{m^3},{}_{\text{o}\text{i}\text{l}}=7355\frac{N}{m^3})$