A spherical cavity of radius 4.50 cm is at the center of a metal sphere of radius 18.0cm. A point charge Q = 5.50 mC rests at the very center of the cavity, whereas the metal conductor carries no net charge. Determine the electric field at a point
(a) 3.0 cm from the center of the cavity and
(b) 6.0 cm from the center of the cavity.