A toroidal solenoid with inner radius 11.6 cm and outer radius of 13.8 cm has a total of 647 windings and carries a current of 4.3 A. What is the magnetic field at distance r=10.4 cm from the center axis? B= What is the magnetic field at distance r=12.7 cm from the center axis? B= What is the magnetic field at distance r=18 cm from the center axis? B=