The Soderberg’s principle

Question

A bar is subjected to fluctuating tensile load from 20 kN to 100 kN. The material has yield strength of 240 MPa and endurance limit in reversed bending  is 160 MPa. According to the Soderberg’s principle, the area of cross-section in mm² of the bar for a factor of safety of 2 is

      (a) 400                                                                (b) 600

      (c) 750                                                                (d) 1000