Answer
$\frac{1}{1000}s$
Work Step by Step
We can find the required shutter speed as follows:
$shutter \space speed=\frac{1}{E(f-number)}$...........eq(1)
We know that
$f-number=\frac{f}{D}$
$\implies f-number=\frac{f}{\frac{f}{8}}=8$
Now we plug in the known values in eq(1) to obtain:
$shutter\space speed=\frac{1}{(\frac{1}{125}s^{-1})(8)}=\frac{1}{1000}s$
