The sum of 4 and 5 has to be equal to : 180 degrees. Because they make a straight angle (which its measure is 180). So we know '4' 108:
[tex]{ 108 }^{ o }+\quad '5'\quad =\quad { 180 }^{ o }\\ '5'\quad =\quad { 180 }^{ o }\quad -\quad { 108 }^{ o }\\ '5'\quad =\quad { 72 }^{ o }[/tex]
5 is equal to [tex]{ 72 }^{ o }[/tex]
