A thin-walled cylindrical pressure vessel of 250 mm internal diameter and 5 mm thickness is subjected to an internal pressure of 2.8 MPa, a twisting moment of 31.36 kN middot m, and an axial tensile load of 45 kN. The ultimate strengths in tension and compression are 210 and 500 MPa respectively. Determine the factor of safety based on the MPS theory.