No, don't use emf = vbl, i was just using that to demonstrate a point!! sorry for the confusion.
The wire is connected to both the conducting rails, thus it creates an effective closed of area. This area of the wire and rail within the magnetic field will be 0.15 * .30 m, which is 0.045m.
So therefore, when the magnetic field is switched off, there will be a change in flux, as you have an area and you have a magnetic field strength.
Multiplying this change in flux by -3 and then dividing by the time taken will give you the required answer.
Remember though, because it is not a closed circuit, there won't be a current, HOWEVER there will be an EMF as EMF can exist without current in an open circuit.
sorry, i'm not very good at explaining things.