The first-order line of 576 nm light falling on a

Question

Solve the all parts of given question:

Question: The first-order line of 576 nm light falling on a diffraction grating is observed at a 12.1° angle.

Part A: How far apart are the slits?

(in m)

Part B: At what angle will the third order be observed?

(in deg)

I need help to determine at what angle the third order be observed.