A site is underlain by a 10 meter layer of dry gravel with unit weight = 20 kN/m3. The lateral stress ratio of the gravel is 0.25. Point A is located 6 meters below the ground surface. Determine the shear stress that acts at point A on a plane inclined 45 degrees counterclockwise from the horizontal. Express your answer in kPa, but do not write the units in the text box (just the numeric answer). If you get a negative answer, do not write the negative sign "-". For example, if you get -12 kPa, simply write 12.