A bimetallic cylindrical bar cross sectional area $1 \: m^2$ is made by bonding Steel (Young's modulus $= 210 \: GPa$) and Aluminium (Young's modulus =$70 \: GPa$) as shown in the figure. To maintain tensile axial strain of magnitude $10^{-6}$ in Steel bar and compressive axial strain of magnitude $10^{-6}$ in Aluminium bar, the magnitude of the required force $P$ (in $kN$) along the indicated direction is

1. $70$
2. $140$
3. $210$
4. $280$