In this question, angle 5 and angle 2 are linear pair. And angles of linear pair are supplementary angles .
Therefore
[tex] \angle 5 + \angle 2=180 [/tex]
And sum of interior angles of a triangle is 180 degree, that is
[tex] \angle 1 + \angle 2 + \angle 3 =180 [/tex]
SInce both the equations have 180 in the right side, left side of both equations are equal too . That is
[tex] \angle 5 + \angle 2 = \angle 1 + \angle 2 + \angle 3 [/tex]
Which gives
[tex] \angle 5=\angle 1 + \angle 3 [/tex]
So the correct option is A .