A brittle material has the properties Sut = 30 kpsi and Suc = 90 kpsi. Using the brittle Coulomb-Mohr and modified-Mohr theories, determine the factor of safety for the following states of plane stress. (a) σx = 25 kpsi, σy = 15 kpsi (b) σx = 15 kpsi, σy = –15 kpsi (c) σx = 20 kpsi, τxy = –10 kpsi (d) σx = –15 kpsi, σy = 10 kpsi, τxy = –15 kpsi (e) σx = –20 kpsi, σy = –20 kpsi, τxy = –15 kpsi