The center of a rectangular area at ground surface has Cartesian coordinates (0, 0), and the corners have coordinates (7, 18). All dimensions are in meters. The area carries a uniform pressure of 150 kPa. Estimate the stresses at a depth of 20 m below ground surface at each of the following locations using the Boussinesq approach: (0, 0), (0, 18), (7, 0), (7, 18), and (12, 28).