Objective question in Capacitors

A parallel plate capacitor of capacitance C is connected to a battery and is charged to a potential difference V. Another capacitor of capacitance 2C is similarly charged to a potential difference 2V. The charging battery is now disconnected and the capacitors are connected in parallel to each other in such a way that the positive terminal of one is connected to the negative terminal of the other. The final energy of the configuration is a) zero b) frac{3}{2}C{V^2} c) frac{{25}}{6}C{V^2} d) .frac{9}{2}C{V^2}