Finding distance between two slits in conditions related to Young's Experiment

[wScott]

Good evening to all you genius people out there, I've been racking my brains for the past 10 minutes and can't come up with anything.

The exact wording of the question:

Describe how you could use light of a known wavelength to find the distance between two slits.

I thought of using distance = wavelength/ sin(theta). But then I realized I'm not given the angle. Got any suggestions for this predicament?

 

[physics girl phd]

Hint -- Do you know what the "far field" pattern looks like when you send monochromatic (and coherent) light through two neighboring slits? the angle will come from something about that.