The purple arrows indicate that side are parallel, so we know that that triangle NMP is the same as triangle NOP. If they are they same then we know that ∠1 and ∠2 equal 60° since the opposing angles equal 60°.
For ∠3 we look at the opposing angle and now know it is 60°. Since ∠3 and the opposing angle make a straight line which equals 180°. We can figure out ∠3 by subtracting 60 from 180 = 120°.
