A diffraction grating having a mere 50 grooves per cm is the object in the optical computer

Question:

A diffraction grating having a mere 50 grooves per cm is the object in the optical computer shown in Fig. 13.41. If it is coherently illuminated by plane waves of green light (543.5 nm) from a He-Ne laser and each lens has a 100-cm focal length, what will be the spacing of the diffraction spots on the transform plane?

Fig. 13.41

$A diffraction grating having a mere 50 grooves per cm$