Both angels are vertical angles. Vertical angles are congruent to each other. Therefore, <AMD ≅ <RMC.
Statement 4: ∆MAD ≅ ∆MRC
Reason 4: AAS Congruence Theorem
Two angles and a non-included side in ∆MAD are congruent to corresponding two angles and a non-included side in ∆MRC. Based on the AAS Congruence Theorem, both triangles are congruent.