You send coherent 550 nm light through a diffraction grating that has slits of equal widths and constant separation between adjacent slits. You expect to see the fourth-order interference maximum at an angle of 66.6∘ with respect to the normal to the grating. However, that order is missing because 66.6∘ is also the angle for the third diffraction minimum (as measured from the central diffraction maximum) for each slit. a. Find the center-to-center distance between adjacent slits. b. Find the number of slits per mm. c. Find the width of each slit.