Hello there!
Today we are dealing with vertical angles which means they must equal each other!
This leads us to be able to set up an equation to solve for x...
3x+50=6x-10
3x+60=6x
60=3x
20=x
So x=20 is the answer. If you wanted to solve for the angle measures, just plug 20 in for x into one of the expressions...
6x-10
6(30)-10
120-10
110
The angles both are 110 degrees, however for the question you asked, the answer is just 20.
I really hope this helps!
Best wishes :)