Parallel Plate Capacitor?

Homework Statement

I am doing a problem in my physics textbook where there is two concentric hollow spheres and the space between them is filled with a dielectric substance. The question asks for the electric energy in this space.

Homework Equations

The only given equation for the C of parallel plate capacitors in my text book is C = A(epsilon)(dielectric constant)/d There is nothing for spherical capacitors
Since the problem has two concentric circles, the plate areas are different. I am not sure if this is still the correct formula to use in this case.

The Attempt at a Solution

Since the change in voltage is given in the text, I need to calculate the capacitance of the 'capacitor' to find the contained electrical energy. The areas are different, so the equation above for C might not apply. How should I proceed from here?

Thank you for helping out! =)

EDIT: I'm sorry, I've figured this out already! I used the energy density of the space, which is the energy(electric energy here) over the volume of the space. Energy density is also equal to 1/2 (dielectric const.)(epsilon)(electric field)^2 so I worked my way to the electrical energy.
Thanks anyway!

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