Two coils A and B each having 1000 turns are placed near each other. When coil B is open circuited and coil A carries a current of 4 A, the flux produced by coil A is 0.4 Wb and 25% of this flux links with all the turns of coil B. Determine the voltage induced in coil B on open circuit, when the current in the coil A is changing at the rate of 3 A/s.