A solenoid of length $60 \mathrm{cm}$ with $15$ turns per $\mathrm{cm}$ and area of cross section $4\times {10}^{-3}{ \mathrm{m}}^2$ completely surrounds another co-axial solenoid of same length and area of cross-section $2\times {10}^{-3}{ \mathrm{m}}^2$ with $40$ turns per $\mathrm{cm}$. Mutual inductance of the system is