Compute each part of given question:

Question: A conducting sphere of radius a is surrounded by a concentric conducting spherical shell of radius r. The inner sphere carries a charge -Q while the outer shell carries a charge +Q.

Part A: Find the electrostatic field energy contained in the region between the two spherical surfaces by integrating the electrostatic energy over this region.

Part B: Find the force as a function of r between the two shells when the inner sphere is held constant and the radius of the outer sphere is expanded.

Any help I can get on this question is greatly appreciated! I'm not too familiar with this question.