Aray of monochromatic light ( f = 5.09 × 10^14 hz) passes from air into lucite at an angle
of incidence of 30.˚.

using a protractor and straightedge, on the diagram, draw the refracted ray in the
lucite.

     Let us consider the air with the index 1 and the lucite with index 2. Using the Snell's Secound Law, we have:


 
     Entering the unknowns, remembering that the air refrective index is 1 and the lucite refrective index is 1.5, comes:


  
     Using the arcsin properties, we get:



Obs: Approximate results, and the drawing is attached

If you notice any mistake in my english, let me know, because i am not native.