A 150 microf capacitor is charged to a potential difference

Question

Compute all parts of given question:

Question: A 15.0 µF capacitor is charged to a potential difference of 900V. The terminals of the charged capacitor are then connected to those of an unchanged 12.0 µF capacitor.

Part I: Compute the original charge of the system.

Part II: Compute the final potential difference across capacitor.

Part III: Compute the final energy of the system.

Part IV: Compute the decrease in energy when the capacitors are connected.

I want help to compute the final potential difference across capacitor.