Single slit diffraction

The distance to the moon can be monitored by laser ranging. A mirror was placed on the moon during the Apollo 11 mission. A laser pulse is shot at the moon and the time it takes for the reflection to return can be used to determine the distance. If light with a wavelength of 625 nm passes through a single slit 1 mm wide, how wide would the beam be on the moon measured from the first minimum on the left of the central maximum to the first minimum on the right of the central maximum?

The average distance to the moon is 384467 kilometers.