6. Figure-7 shows the cross-section of a hollow cylinder of inner radius a - 4.00 cm and outer radius c = 9.00 cm. A uniform current density of 2.50 A/ cm2 flows through the cylinder parallel to its axis. Figure 7 a) What is the magnitude of the magnetic field at r = 2.00 cm? Explain or show your work. b) What is the magnitude of the magnetic field at b = 6.50 cm? c) What is the magnitude of the magnetic field at d = 15.0 cm