Can someone walk me through this problem?

Can someone walk me through this problem? I know the answer is 495 nm but I don't know how to do it:(

In two separate double slit experiments, an interference pattern is observed on a screen. In the first experiment, violet light (l = 708 nm) is used and a second-order bright fringe occurs at the same location as a third-order dark fringe in the second experiment. Determine the wavelength of the light used in the second experiment.