A Pair of Narrow Slits That Are $1.8 \mathrm {~mm}$ Apart Is Illuminated by a Monochromatic Coherent Light Source

Multiple Choice

A pair of narrow slits that are $1.8 \mathrm {~mm}$ apart is illuminated by a monochromatic coherent light source. A fringe pattern is observed on a screen $4.8 \mathrm {~m}$ from the slits. If there are $5.0$ bright fringes/cm on the screen, what is the wavelength of the monochromatic light?

A) $750 \mathrm {~nm}$
B) $600 \mathrm {~nm}$
C) $650 \mathrm {~nm}$
D) $700 \mathrm {~nm}$
E) $550 \mathrm {~nm}$