$3\mathrm{.}2$ A reinforced concrete rectangular beam is subject to design loads that result in a maximum bending moment, $=360ft-$kip.

The maximum beam width is limited to $18$ and the reinforcing bar area, $As=3\mathrm{.}16i{n}^2.$

Determine the minimum effective depth of the beam so that its bending strength is larger than the required moment.

Material properties are:

$fc=5$ksi

$fy=60$ksi