4. (8 points total) An ASTM 30 cast iron has an elongation at fracture of 2.0% of the original length. It experiences a plane stress state given by = 120 MPa, y = -160 MPa, and Txy = 80 MPa. (a) (4 points) Determine the factor of safety using the Coulomb-Mohr theory and the Modified-Mohr theory. Compare the two factors of safety, and comment on whether their relative values match your expectation given what you know of these theories. (b) (4 points) Plot to scale the stress failure envelope for this material and the coordinates of the given stress state. By drawing the corresponding load line, estimate the factor of safety for each method by graphical measurement.