Double Slit Problem: Solve for D2-D1 with 500nm Wavelength

[knox_122]

here the problem:

In the Young Double Slit experiment, alternatingbands of bright and dark regions are produced on the screen. At the dark band shown in the picture below, on slit is a closer than the other slit: In other words, D1 is less than D2, Find D2-D1, Assuming that the light has a wavelength of 500nm.


The Picture he shows, he said is not to scale so it won't help. there are no other measurements listed. How do i go about figuering this out?

 

[lightgrav]

I hope there's an angle scale in the pic.

Distance between slit centers "d" makes fringes (bands) that are angle-dependent, as m \lambda = d sin \theta