Answer:
1. Given.
2. Definition of congruent segments.
3. Segment Addition Postulate.
4. Substitution Property of Equality.
5. Transitive Property of Equality.
6. Subtraction Property of Equality.
7. Definition of congruent segments.
Explanation:
Statement 1

Reason: Given.
Statement 2

Reason: Definition of congruent segments.
Congruent segments are segments that have the same length.
Statement 3

Reason: Segment Addition Postulate.
A line segment divided into smaller pieces is the sum of the lengths of all those smaller segments.
Statement 4

Reason: Substitution Property of Equality.
For all numbers a and b, if a=b, then a may be replaced by b in any equation or expression.
Statement 5

Reason: Transitive Property of Equality.
For all numbers a, b and c, if a=b and b=c, then a=c.
Statement 6

Reason: Subtraction Property of Equality.
For all numbers a, b and c, if a=b, then a-c=b-c.
Statement 7

Reason: Definition of congruent segments.
Congruent segments are segments that have the same length.