Question 173426
Not having the diagram, there is no way to tell for certain, but I suspect that you need to demonstrate, either by use of the 5 postulates, or subsequent theorems already proven, that Angle 1 is equal in measure to either Angle 2 or Angle 3.  Then show that Angle 4 is equal in measure to either Angle 3 or Angle 2.  Then you can use the principle that things equal to equal things are themselves equal.  If you know that a = b and c = d, then if you can demonstrate that b = c somehow, you know that a = d.