Help with physics please?!?

Question

A diffraction grating with 403 lines/mm is 1.00 m in front of a screen. What is the wavelength of light whose first-order maxima will be 17.7 cm from the central maximum on the screen?

Answer 1

First calculate the angle .

TanΘ = 17.7x10^-2/1.00

Θ = 10.03739409°

dsinΘ =n(wavelength )

403 lines per mm = 403000 lines per meter .

(1/403000)sin10.03739409 = 1(wavelength )

Wavelength = 432nm