Few candidates attempted this question and majority of those who did performed poorly.  Many candidates misconstrued the question and were calculating critical angle.

The expected answer is:

Diagram

 

 

n  =  sin θ                    =    sin θ    =  tan θ                                                      
      Sin (90 – θ)                  cos θ
                                                                                               
1.54   =   tan θ                                                                                                
θ   =    57o