A bicycle generator rotates at 1875 rad/s, producing an 18.0 V peak emf. It has a 1.00 cm by 3.00 cm rectangular coil in a 0.640 T field. It is driven by a 1.60 cm diameter wheel that rolls on the outside rim of the bicycle tire. If the sophisticated generator can vary its own magnetic field, what field strength will it need at 5.00 m/s to produce a 9.00 V maximum emf?