$(4$ points$)$

$4-$ Find vertical stress increase below center of a rectangular footing at a depth of $z=5ft,$ length $=5\mathrm{.}5ft,$ width$=4\mathrm{.}5$ ft under a pressure $($q$)$ of $1\mathrm{.}0$ ksf on the footing. $(2$ points$)$