In the figure, both angles are the same since there is a little line on both sides of the figure. That means that they are the same in length. This also tells us that both angles will have the same measure.
We can write an equation as:
3x = 5x - 30
Solve for x:
3x = 5x - 30
~Subtract 5x to both sides
3x - 5x = 5x - 5x - 30
~Simplify
-2x = -30
~Divide -2 to both sides
-2x/-2 = -30/-2
~Simplify
x = 15
Best of Luck!