Answer
$\Delta S=8.8mm$
Work Step by Step
We know that:
$E=\frac{\sigma}{2\epsilon_{\circ}}$
We plug in the known values to obtain:
$E=\frac{0.10\times 10^{-6}}{2(8.85\times 10^{-12})}=5649.71\frac{N}{C}$
We also know that
$\Delta S=\frac{V}{E}$
We plug in the known values to obtain:
$\Delta S=\frac{50}{5649.71}=8.8\times 10^{-3}=8.8mm$