The correct answer is: C. Net area in both cases
Bending compressive and tensile stresses are calculated based on the net area of the cross-section of the beam. The net area is the area of the cross-section of the beam minus the area of any holes or cutouts. This is because the net area is the only area that is actually resisting the bending forces.
The gross area is the total area of the cross-section of the beam. This is not used in calculating bending stresses because it includes the area of any holes or cutouts, which are not resisting the bending forces.
Here is a diagram that shows the difference between the net area and the gross area:
[Diagram of a beam with a hole in it, showing the net area and the gross area]
The net area is the shaded area, and the gross area is the unshaded area.
I hope this explanation is helpful! Let me know if you have any other questions.