For the section shown below compute the followings:

$($a$)$ The minimum required reinforcement ratio

$($b$)$ The strain $({}_t)$ in the reinforcing steel

$($c$)$ The design strength, $\frac{O}{M_n}$

$f_c^{\text{'}}=3\mathrm{.}5$ksi and $f_y=60$ksi