Answer:
Given:
,
,
,
formed by two intersecting segments.
In the given figure;
Linear pair states that a pair adjacent angle formed when two lines intersect.
Then by definition of linear pairs,
and
forms a linear pair
Also,
and
forms a linear pair.
Linear pair postulates states that the two angle that forms a linear pair are supplementary(i,e add up to 180 degree).
Then by linear pair postulates;

and

Substitution property of equality states that if x =y then, x can be substituted in for y or vice -versa.
then by substitution property of equality:

Addition property of equality states that:
if x =y, then x + z = y+ z
By addition property of equality:
hence proved!