$2\mathrm{.}2$ Consider a rectangular reinforced concrete beam with an effective depth of $36$ in$.$ reinforced with $4$#$9$ bars. $f_c^{\text{'}}=4,000,$ and $f_y=60,000$ psi. Determine $M_R$ using Method I or II for the following cases:

$($a$)b=14$ in$.$

$($b$)b=16$ in$.$

$($c$)b=18$ in$.$

$($d$)b=20$ in$.$