supplemantary angles add up to 180 degree.
[tex]\begin{gathered} \angle CDE\text{ and }\angle EDF\text{ are supplementary angles } \\ m\angle CDE=2x+6 \\ m\angle\text{FDE}=x-9 \\ 2x+6+x-9=180 \\ 3x-3=180 \\ 3x=183 \\ x=\frac{183}{3} \\ x=61\text{ } \end{gathered}[/tex]
