Answer:
X = 12
IM not sure witch exsterio angle you are looking for but here is how you do it.
Step-by-step explanation:
[tex](5x -6 ) + 3x + 90 = 180\\x = 12\\[/tex]
That makes the exstieror angle of 3x = 144
5(12) - 6 = 126
90 = 90
