In the question you have to assume that Lift does indeed equal weight. Thus you get (120000-41667)/500000 = 0.15666
Now using small angle approximation sin a = tan a = opp/adj
Thus you have a ratio of 15.6/100 or 15.7%.
Tan-1 and Sin-1 don't come into it.
I expect to see one in the exam on Monday, but with different numbers