$5.$ A steel beam section $($E$=200$GPa$)$ with a width of $0\mathrm{.}2$m$,$ height of $0\mathrm{.}1$m and a length, L of $3$m

is used to span a river. Determine the deflection of the bridge when a person with a mass of

$90$kg stands on the middle of it$.$