Single Slit Diffraction

Monochromatic light of wavelength 633nm falls on a slit. If the between the first bright fringes on either side of the central maximum is 19.5 degrees, what is the slit width?

The maxima of a diffraction pattern occur at:

mλ=(d/2)sin(θ)

For the first maxima on either side of the centre, m=+1. If the angle between these two is 19.50, then the two maxima occur at θ=+(19.5/2)^o

d=2λ/sin(9.75sup]o)

d=7500nm