A very long, straight solenoid with a cross-sectional area of 6.25cm ^2 is wound with 30 turns of wire per centimeter, and the windings carry a current of 0.230 A . 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 5.20 x 10 ^-2 s.
What is the average induced emf in the secondary coil?