A Helium-Neon Laser $\lambda$ = 6328 Nm)is Used to Calibrate a Diffraction Grating

Multiple Choice

A helium-neon laser ( $\lambda$ = 632.8 nm) is used to calibrate a diffraction grating.If the first-order maximum occurs at 20.5 $\degree$ ,what is the line spacing,d?

A) 1.81 *10^-6 m
B) 1.00 *10^-5 m
C) 1.00 *10^-4 m
D) 1.31 *10^-6 m
E) 6.76 *10^-7 m