seilinger et al$.,$ Rev. Mod. Phys$.60,1067(1998)$ carried out a double$-$slit ezxperiment wit hneutrons with a wavelength of $2$ nm$.($a$)$ what was the speed of these neutrons? $($b$)$ the two slits were $22$ m and $23$ m wide and were seperted by a distance of d $=104$ m$.$ The detection plane was locatecd $5$ m downstream