Problem $1(20$ points$)$: For each section illustrated, locate the neutral axis, find the distances from the neutral axis to the top and bottom surfaces, and calculate the second moment of area, the. Consider that the section is transmitting a positive bending moment of $M_z=2kN.m($problem $1$a$)$ and $M_z=10$kip. in $($Problem $1$b$)$ about the z $-$axis. Determine the resulting stresses at the top and bottom surfaces.

$1($D$).$