the picture in the attached figure
we know that
In a triangle, each exterior angle has two remote interior angles. The remote interior angles are just the two angles that are inside the triangle and opposite from the exterior angle.
in this problem
∠5=∠2+∠3
∠4=∠1+∠2
∠6=∠+∠3
therefore
the answer is
∠5=∠2+∠3