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 principle, the area of cross-section in $mm^2$ of the bar for a factor of safety of $2$ is

- $400$
- $600$
- $750$
- $1000$