Two charged concentric spheres have radii of 9.6 and 15.1 cm. The charge on the inner sphere is 4.09 multiplied by 10-8 C and that on the outer sphere is 2.10 multiplied by 10-8 C.
(a) Find the electric field at r = 12.4 cm.
(b) Find the electric field at r = 19.9 cm.