A $3\mathrm{.}44-nF$ parallel$-$plate capacitor is charged to an initial potential difference $V_i=100V$ and is then isolated. The dielectric material between the plates is paper, with a dielectric constant of $3\mathrm{.}7.$

$($a$)$ How much work is required to withdraw the paper sheet? $J$

$($b$)$ What is the potential difference of the capacitor after the paper is withdrawn?

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