Two coaxial solenoids are made by winding thin insulated wire over a pipe of cross-sectional area $A = 10\,\text{cm}^2$ and length $= 20\,\text{cm}$. If one of the solenoids has $300$ turns and the other $400$ turns, their mutual inductance is ($\mu_0 = 4\pi \times 10^{-7}\,\text{T}\cdot\text{m/A}$)