Solving a problem in physics section 35 paragraph 90 qu

90. In the experiment of Davisson and Germer, discovered the diffraction pattern of the electron beam in the reflection of the natural diffraction grating - a single crystal of nickel, it appears that in a direction making an angle α = 55 ° with the direction of the incident beam, there is a maximum reflection of the fourth order in the electron kinetic energy T = 180 eV. Determine the distance d between the atomic planes in nickel.