Two coaxial solenoids are made by winding thin insulated wire over a pipe of cross sectional area $$A = 10\ cm^2$$ and length = 20 cm. If one of the solenoids has 300 turns and the other 400 turns, their mutual inductance is $$(\mu_0 = 4\pi \times 10^{-7}\ T\ m\ A^{-1})$$

A

$$2.4\pi \times 10^{-5}\ H$$

B

$$4.8\pi \times 10^{-4}\ H$$

C

$$4.8\pi \times 10^{-5}\ H$$

D

$$2.4\pi \times 10^{-4}\ H$$