Check the picture below.
[tex]4x~~ = ~~\cfrac{120~~ + ~~2x}{2}\implies 8x=120+2x\implies 6x=120 \implies x=\cfrac{120}{6} \\\\\\ x=20~\hfill \stackrel{\measuredangle 4x}{4(20)=80^o}~\hfill \underset{180~~ - ~~4x}{\stackrel{\measuredangle AED}{180^o-80^o=100^o}}[/tex]
