A point charge q = 3.0C is located at the centre of a spherical layer of uniform

Question:

A point charge q = 3.0μC is located at the centre of a spherical layer of uniform isotropic dielectric with permittivity e = 3.0. The inside radius of the layer is equal to a = 250 ram, the outside radius is b – 500 ram. Find the electrostatic energy inside the dielectric layer.