Answer
We would also need to know the angle $\theta$ between the direction of the magnetic field and the surface area in order to calculate the average magnetic field through the surface.
Work Step by Step
$\Phi = B~A~cos~\theta$
Although we know the magnetic flux and the area, we would also need to know the angle $\theta$ between the direction of the magnetic field and the surface area in order to calculate the average magnetic field through the surface.
