Two coils A and B having turns 300 and 600 respectively are placed near each other, on passing a current of 3.0 ampere in A, the flux linked with A is  $1.2\times {10}^{-4}\mathrm{weber}$ and with B it is $9.0\times {10}^{-5}\mathrm{weber}$ . The mutual inductance of the system is

• A

  $2\times {10}^{-5}\text{ henry }$

• B

  $3\times {10}^{-5}\text{ henry }$

• C

  $4\times {10}^{-5}\text{ henry }$

• D

  $6\times {10}^{-5}\text{ henry }$