Young's experiment is performed with light of wavelength 502 nanometer from excited helium atoms. Fringes are measured carefully on a screen 1.40 meter away from the double slit, and the center of the 20th fringe (not counting the central bright fringe) is found to be 10.2 millimeter from the center of the central bright fringe.
Compute what the separation of the two slits?
Answer in mm.