Now that we have calculated the necessary section properties, we can compute the normal and shear stresses acting at $B$, $\mathrm{3} \mathrm{in}\mathrm{.}$ above the neutral axis (the $z$ axis for this configuration).

Normal stress
due to bending   $$\begin{gathered} {\sigma }_x=-\frac{My}{I} \\ =-\frac{(150 kip-ft)(3 in.)(12 in./ft)}{560.03125 in{.}^4}=-9.64 ksi \end{gathered}$$