In yang's double slit experiment , the slit are separated by $0.25$ mm and the screen is placed 1.4 m away. The distance the control bright fringe and the fourth bright fringe is measured to be 1.2 cm determine the wave length of light used in the experiment

Question

$\begin{array}{1 1} 6 \times 10^7\;m \\ 6 \times 10^6\;m \\ 6 \times 10^{-7}\;m \\ 6 \times 10^{-6}\;m \end{array} $