Question

A)How many slits per centimeter does a grating have if the third order occurs at a 17° angle for 629 nm light?

B) What is the highest spectral order that can be seen if a grating with 6500 slits per cm is illuminated with 633 nm laser light? Assume normal incidence ( $LaTeX: \theta=90^o$ θ = 90 o).

Hint: round down and write it as an integer.