Two angles are called supplementary when their measures add up to 180 degrees..
Therefore, we have,
[tex]<\text{ABC}+<\text{CBD}=180[/tex]
Substituting the values we get,
[tex]\begin{gathered} 4x-19+39=180 \\ 4x+20=180 \\ 4x=180-20=160 \\ 4x=160 \\ x=\frac{160}{4}=40 \end{gathered}[/tex]
Thus, the required value of x = 40
