Answer:
x = 21
Step-by-step explanation:
We know: The sum of the triangle angle measures is 180°.
Therefore we have the equation:
[tex]100+3x+x-4=180\qquad\text{combine like terms}\\\\(3x+x)+(100-4)=180\\\\4x+96=180\qquad\text{subtract 96 from both sides}\\\\4x=84\qquad\text{divide both sides by 4}\\\\x=21[/tex]
