\textbf{196-} In Young's experiment, the time difference for light to travel from two slits to the center of the fifth dark fringe is $6\times10^{-15}$ seconds. What is the wavelength of the light used in the experiment in nanometers? $\left(C = 3\times10^{8}\ \dfrac{\text{m}}{\text{s}}\right)$
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(1) $550$ \hfill (2) $500$ \hfill (3) $450$ \hfill (4) $400$
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