A Parallel Plate Capacitor with Radius 21 Cm Is Connected $\varOmega$

A parallel plate capacitor with radius 21 cm is connected in series 15-V battery.A switch is thrown which causes the capacitor to discharge through a 150- $\varOmega$ resistor.What is the magnetic field 1.0 cm from the axis defined by the centers of the plates at this time?

A) 1.0 * 10^-12 T
B) 3.1 * 10^-12 T
C) 2.1 * 10^-11 T
D) 4.5 * 10^-9 T
E) You need to know the separation of the plates.