Problem $3$:

A hollow$-$core concrete plank is subjected to bending moment magnitudes $M_2=50$kip$*ft$ and $M_y=20$kip$*ft,$ acting in the directions shown in Figure P$8\mathrm{.}61.$ The cross$-$sectional dimensions are $b=24$ in$.,h=12$ in$.,d=7$ in$.,$ and $a=5\mathrm{.}5in.$ Determine

$($a$)$ the bending stress at $B.$

$($b$)$ the bending stress at $C.$

$($c$)$ the angle $$ that the neutral axis makes with the $+z$ axis. Note that positive $$ angles rotate clockwise from the $+z$ axis.