∡1 and ∡2 are congruent. If ∡3 is 68°; ∡1 = 112° (180° - 68°); ∡4 = 68° (∡3 and ∡4 are vertical angles, therefore, they are congruent, also, 180° - 112° =68°);∡2 = 112° (∡1 and ∡2 are vertical angles, therefore, they are congruent, also, 180° - 68° = 112°)
∡3 and ∡1 are linear pair; ∡3 and ∡2 are linear pair.
∡4 and ∡1 are linear pair; ∡4 and ∡2 are linear pair.
∡3 and ∡4 are vertical angles therefore, they are congruent.
∡1 and ∡2 are vertical angles therefore, they are congruent.
