$P_{i}=76 \mathrm{cm}$ of $\mathrm{Hg}$

$V_{i}=5 A$

Finally

$P_{f}=(76)-(48-x)=(28+x) \mathrm{cm}$ of $\mathrm{Hg}$

$V_{f}=x A$

since, temperature remains constant

$\therefore P_{i} V_{i}=P_{f} V_{f}$

$\Rightarrow 76 \times 5 A=(28+x) \times A$

$\Rightarrow x^{2}+28 x-380=0$

$\Rightarrow(x+38)(x-10)=0$

$\Rightarrow x=10 \mathrm{cm}$ or $x=-38 \mathrm{cm}$

$x=-38$ rejected since $x$ can't $be -ve$