Computer Study—comparison of cantilever and portal methods with an exact analysis. (a) Determine the moments, shear, and axial forces in the members of the frame in Figure P13.18, using the portal method. (b) Repeat the analysis using the cantilever method. Assume the area of the interior columns is twice the area of the exterior columns. (c) Compare the results with an exact analysis using a computer software. Use E = 29,000 kips/in.2 for all members; A = 12 in.2 and I = 600 in.4 for beams and interior columns; A = 8 in.2 and I = 400 in.4 for exterior columns.