You are given a slide with two slits cut into it and asked how far apart the slits are. You shine white light on the slide and notice the first-order color spectrum that is created on a screen 4.40 m away. On the screen, the red light with a wavelength of 688 nm is separated from the violet light with a wavelength of 391 nm by 6.60 mm. What is the separation of the two slits?