Answer:
Step-by-step explanation:
Statement                                        Reason
1. ∠4 is an exterior angle of ΔABC                     Given
2. ∠3 and ∠4 form a linear pair                   Linear pair property
3. ∠3 is supplementary to ∠4                   Straight line property
4. m∠3+m∠4=180°                         ∠3 is supplementary to ∠4   Â
5. m∠1+m∠2+m∠3=180°                      Triangle sum theorem
6.m∠1+m∠2+m∠3= m∠3+m∠4                  Statement 4 and 5
7. m∠1+m∠2=m∠4                           Subtraction property