A very long, straight solenoid with a cross-sectional area of 6.00cm squared is wound with 40 turns of wire per centimeter, and the windings carry a current of 0.250A . A secondary winding of 2 turns encircles the solenoid at its center. When the primary circuit is opened, the magnetic field of the solenoid becomes zero in 5.00×10?2s . What is the average induced emf in the secondary coil?