You have the next measures of angles:
[tex]m\angle\text{ZFDE}=(3x-15)[/tex][tex]m\angle ZFDB=(5x+59)[/tex]
And you need to find the value that makes the angles supplementary. It means that you need to find the value of x that makes that: the sum of the angles has to be 180º
[tex]m\angle ZFDE+m\angle ZFDB=180º[/tex]
Then you have:
[tex](3x-15)+(5x+59)=180[/tex]
You clear the x, as follow:
[tex]3x+5x-15+59=180[/tex][tex]8x+44=180[/tex]Then so, the value of x that makes that ZFDE and ZFDB are supplementary is x=17
