Problem $4\mathrm{.}21$ Select reinforcing bars for the beam shown if $M_u=150ft-k,f_y=60,000$ psi, and $f_c^{\text{'}}=4000$ psi. $($Hint: Assume that the distance from the c$.$g$.$ of the tensile steel to the c$.$g$.$ of the compression block equals $0\mathrm{.}9$ times the effective depth, $d,$ of the beam.$)$ After a steel area is computed, check the assumed distance and revise the steel area if necessary. Is $lo{n}_{t}0\mathrm{.}005?$