A square, single-turn coil 0.20 m on a side is placed with its plane perpendicular to a constant magnetic field. And emf of 18mV is induced in the coil winding when the areas of the coil decreases at the rate of 0.10 m^2/s. What is the magnitude of the magnetic field. (Note the change in flux can be due to a change in magnetic field of a change in area. Note that the unit of Tesla can be Volt sec / m^2. )