1. The problem statement, all variables and given/known data In a double-slit experiment, the third order bright fringe is 15 mm from the central fringe. What is the distance of the first (zero-th order) dark fringe from the central maximum? 2. Relevant equations (m+.5)(lambda) = dsin(theta) => dark fringe m(lambda) = dsin(theta) => bright fringe 3. The attempt at a solution I honestly don't know. Like, there's no angle or wavelength. The most I've come up with is 15 mm divided by 3 (because it's the third) and getting 5 mm. I seriously don't know.