Example $14\mathrm{.}2$: What is the minimum depth required for a foundation to transmit a pressure

$60k\frac{N}{m^2}$ in a cohesionless soil with $=18k\frac{N}{m^3}$ and $=18?$ What will be the bearing

capacity if a depth of $1\mathrm{.}5$ m is adopted according to Rankine's approach?