When Using 529-Nm Light, How Far Is the Adjustable Mirror

When using 529-nm light, how far is the adjustable mirror of a Michelson interferometer moved when 600 fringe shifts are counted? A fringe shift occurs when the intensity goes from bright to dark or when it goes from dark to bright.

A) 1.58 * 10^-4 m
B) 7.94* 10^-5 m
C) 9.90 *10^-6 m
D) 3.97 * 10^-5 m