Answer:
x=50
Explanation:
Since Line AB and Line CD are parallel, Angle AFG is supplementary to Angle CGF. So then x+3x-20=180. Then you just solve for x.
Combine like terms-> 4x-20=180
Add 20 to both sides-> 4x=200
Divide both sides by 4-> x=50
Hope this helps!
Feel free to ask if you still don't understand something