Look at the picture.
[tex\alpha+\beta=180^o[/tex] - supplementary angles
Therefore we hve the equation:
[tex](14x-6)+(15+5x)=180\\\\(14x+5x)+(-6+15)=180\\\\19x+9=180\qquad\text{subtract 9 from both sides}\\\\19x=171\qquad\text{divide both sides by 19}\\\\\boxed{x=9}[/tex]
