Laser light with a wavelength of 665 nm illuminates a pair of slits at normal incidence. What slit separation?

Laser light with a wavelength of 665 nm illuminates a pair of slits at normal incidence. What slit separation will produce first-order maxima (i.e. m=1) at angles of plus or minus 9 degrees from the incident (or straight through) direction?give answer in micrometres.