The missing statements and reasons are: 3. m∠DFG + m∠DEF = 180° 4. definition of supplementary.
What are supplementary angles?
Supplementary angles are two angles whose measures add up to 180 degrees, which implies that when the sum equals 180 degrees, then they are supplementary.
Given that, m∠DFE ≅ m∠DEF based on definition of congruence, and m∠DFG + m∠DFE = 180° based definition of supplementary.
Applying substitution, we have:
m∠DFG + m∠DEF = 180°
Therefore, ∠DFG and ∠DEF are supplementary based on the definition of supplementary.