Next, consider the area between this line and the furthest extreme of the cross section (i.e., extending away from the neutral axis).

$Q$ is the moment of the shaded area about the neutral axis:

The transverse shear force $V$ acts in the $-x$ direction. To calculate the transverse shear stress, use the elastic shear stress formula:

$\tau =\frac{VQ}{It}$

To find $\tau$, first slice through the cross section at $B$, parallel to the neutral axis. The width of the cross section at this location is the dimension $t$.