Two coaxial solenoids are made by winding thin insulated wire over a pipe of cross-sectional area `A=10 cm^(2)` and length =20cm. If one of the solenoid has 300 turns and the other 400 turns, their mutual indcutance is
A. `2.4 pi xx 10^(-5)H`
B. `4.8 pi xx 10^(-4)H`
C. `4.8 pi xx 10^(-5)H`
D. `2.4 pi xx 10^(-4)H`