So, you put the values on the other sides of the vertical angles, so you get a set of interior angles (can't remeber word at the moment)
Make the angles equal to 180.
So equation looks like 3x+11+5x+9=180.
Now combine like terms, get 8x+20=180.
Subtract 20 from both sides and get 8x=160.
Divde both sides by 8 and get your answer of x= 20
Hope this helps