17. A part is made of cast iron with the following strength properties, Sut 15 ksi and Suc 109 ksi. Suppose at the candidate trouble spot a static stress state exists such that = 12 ksi and oy = 10 ksi. By an appropriate failure theory, the safety factor is n 18. Repeat the preceding problem, but now assume that the stress state is 0-12 ksi and oy -10 ksi. n = 19. Repeat the preceding problem, but now assume that the stress state is = 12 ksi and = -10 ksi. n =