Well, for starters, we know that a straight line equals 180°. Since all of those angles are within that straight line, we know that they add up to it.
Aka, all of them add up to 180.
How do we write that out?
(5x) + (3x+30) + (2x+10) = 180
And now you just solve for x.
10x + 40 = 180
10x= 140
x=14.
Hope I helped! Comment & tell me if I did <3