Two angles on a straight line are always supplementary angles, they add up to 180º.
Then, the given angles add up to 180º:
[tex]4x+(2x-12)=180[/tex]
Use the equation above to solve x:
[tex]\begin{gathered} 4x+2x-12=180 \\ 6x-12=180 \\ \\ \text{Add 12 in both sides of the equation:} \\ 6x-12+12=180+12 \\ 6x=192 \\ \\ \text{Divide both sides of the equation into 6:} \\ \frac{6}{6}x=\frac{192}{6} \\ \\ x=32 \end{gathered}[/tex]
Then, the value of x is 32
