Solving a problem in physics section 2 point 60 optics

60. The narrow parallel beam of X-rays with a wavelength λ = 245 nM drops on the brink of a single crystal of natural rock salt. Determine the distance d (Fig.) Between the atomic planes of a single crystal, if the second-order diffraction peak is observed in the fall of radiation to the surface of the single crystal at a glancing angle θ = 61 °.