Change in energy of a capacitor

A certain capacitor has a capacitance of 5.0 μF. After it is charged to 5.0 μC and isolated, the plates are brought closer together so its capacitance becomes 10μF. The work done by the agent is about:

I assumed Qfinal = Qinitial since I believe there is still some separation, right (it’s still a capacitor, isn’t it?)? So, I did W = ΔU and let Uf = (1/2C)Q2 and I did Ui = (1/2C)Q2 and I increased the capacitance by 2 since area is doubled, right? But how does the distance of separation change?

Any help please?

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