$3\mathrm{.}19$ A small gravity retaining wall $($Figure $3\mathrm{.}81)$ is used to accommodate a $4\frac{1}{2}$ foot drop in elevation. Determine the wall's factor of safety against overturning.

${}_{\text{c}\text{o}\text{n}\text{c}\text{r}\text{e}\text{t}\text{e}}=150\frac{\text{\#}}{f{t}^3}$ and the equivalent fluid density

${}^{\text{'}}=40\frac{\text{\#}}{f{t}^3}$