Two coaxial solenoids are made by winding thin insulated wire over pipe of cross-sectional area $\mathrm{A}=10{\mathrm{cm}}^2$ and length = 20$\pi$ cm. If one of the solenoid has 300 turns and the other 400 turns, their mutual inductance (in H) is $\mathrm{X}\times {10}^{-4}\mathrm{H}$ . The value of ‘X’