Suppose that following the CME it is found that at an altitude of 2500 m the electric field has magnitude 1300 N/C and at an altitude of 1500 m the magnitude is 3600 N/C. In both cases the direction of the electric field is vertically toward the earth's surface. Find the net amount of charge (also indicate the sign of the charge) contained in a cube with horizontal faces at altitudes of 2500 and 1500 m. Assume that the surface of the earth is flat and horizontal. Give your answer in the form of "+/-a.bc x 10^(x) C".