The two lines don't change direction when they intersect, so that means the two angle measures are equivalent.
You could write [tex]4x + 20 = 3x + 55[/tex].
To make this easier, you can move the numbers with variables to one side of the equation, and the numbers without variables to the other. Know that when a number is moved to the other side, it becomes the opposite of what it currently is.
[tex]4x + 20 = 3x + 55[/tex]
--> [tex]4x - 3x + 20 = 55[/tex]
---> [tex]4x - 3x = 55 - 20[/tex]
----> [tex]x = 35[/tex]
The value of x is 35.
