Question

If (angle)1 = 7x and (angle)4 = 3x + 20, what is the value of x?

Answer 1

The value of x is 5. Angle one and four are vertical. You can do this by writing 7x = 3x + 20. Isolate the variable by moving 3x to the other side. If you do this, 3x becomes negative, and you end up with 7x-3x = 20 --> 4x = 20.
x=5.

Answer 2

$m\angle 1=m\angle4\\\\therefore:\\\\7x=3x+20\ \ \ |-3x\\\\4x=20\ \ \ |:4\\\\x=5$

Answer: 5