A monochromatic light of wavelength 587.5nm illuminates a slit of width 0.75mm. At what distance from the slit should a screen be placed so that the first dark fringe is at 0.85mm from the center of the diffraction pattern?

Answer 1

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/sinslit.html
solve for d.