Q. A laser with wavelength d/8 is shining light on a double slit with slit separation 0.3 {rm mm}. This results in an interference pattern on the screen a distance L away from the slits. We wish to shine a second laser, with a different wavelength, through the same slits.

What is the wavelength lambda_2 of second laser that would place its second maximum at the same location as the fourth minimum of the first laser, if d = 0.3 {rm mm}?

Express the answer in millimetres.