Young's fringes, produced by monochromatic laser light passing through slits 0.60mm apart, are viewed on a screen. The distance accrose 20 fringe spacings on the screen is 58mm. When the screen is moved 0.80m away from the slits, the distance across 20 fringe spacings becomes 74mm.
Y = D(lamda) / d
Y = Fringe Spacing
D = Distance from slits to screen
d = spacing between slits
(lamda) = Wavelength