An ASTM cast iron, grade 30 (see Table A24), carries static loading resulting in the stress state

Question:

An ASTM cast iron, grade 30 (see Table A–24), carries static loading resulting in the stress state listed below at the critical locations. Choose the appropriate failure locus, plot it and the load lines, and estimate the factors of safety analytically and graphically.
(a) σA = 20 kpsi, σB = 20 kpsi.
(b) τx y = 15 kpsi.
(c) σA = σB = −80 kpsi.
(d) σA = 15 kpsi, σB = −25 kpsi.