$4.$ A double$-$slit is illuminated with monochromatic light and the pattern shown below is observed on a viewing screen located $215$ cm from the plane of the slits. Each slit has a width of $\backslash (40\mathrm{.}0\backslash$mu $\backslash$mathrm$\{$~m$\}\backslash )$ and the centers of the two slits are separated by $\backslash (250\backslash$mu $\backslash$mathrm$\{$~m$\}\backslash ).$ The separation between adjacent interference fringes is measured to be $5\mathrm{.}63$ mm $.$

a$)$ What is the wavelength of the light used? Is this wavelength in the visible portion of the electromagnetic spectrum? If so$,$ what color would it correspond to$?$

b$)$ Use the wavelength calculated in part a$)$ to calculate the distance between the first two diffraction minima located to the right of the central diffraction maxima.

Closely$-$spaced dark "interference" fringes

Widely$-$spaced dark "diffraction" fringes