Only the reasons need be given here, as the statements are already given in your figure.
Given
Given
Given
Definition of congruent line segments
Symmetric property of congruence
Addition and substitution properties of equality*
Segment addition theorem
Definition of congruent line segments
AAS congruence postulate
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* The addition property says if A=B, then A+C=B+C. The substitution property further says if C=D, then A+C=B+D (D can be substituted for C). IMO, both properties are needed together to get from A=B and C=D to A+B=C+D.