Answer:
The formula for induced EMF is ε = BLv
The B is the magnetic field of the earth. I will solve this problem with a value of 1 X 10-4 T for the accepted value of the earths magnetic field. However, with that said, your book may use a different value. If that is the case, this answer will be wrong, but the formula works. All you will need to to is find the value for the earth's magnetic field that your book wants you to use, and substitute for 1 X 10-4 T.
ε = BLv
ε = (1 X 10-4)(1.8 X 104)(7.8 X 103) = 14040 V
Again, if your book does not like this answer, use this equation
ε = (B)(1.8 X 104)(7.8 X 103) and just plug in a different value for B found in your text