Answer:
7.By transitive property of equality
8.By substitution property
9.Subtraction property of equality
10.Converse of angles congruence postulate.
Explanation:
We are given that
, angle 2 and angle 3 are supplementary and angle 1 and angle 4 are supplementary.
We have to prove that

We have to write missing statements in given proof.
1.

Given
2.

Angle congruence postulate
3.Angle 2 and angle 3 are supplementary.
Given
4.

By definition of supplementary angles
5.Angle 1 and angle 4 are supplementary
Given
6.

By definition of supplementary angles
7.

By transitive property of equality
8.

By substitution property
9.

Subtraction property of equality
10.

Converse of angle congruence postulate