Measure of Angle 2 = 100 degrees
measure of Angle 6 = 100 degrees
Since angle 2 and angle 6 are both 100 degrees, this makes them congruent angles. They are also corresponding angles as well.
The fact we have corresponding angles that are congruent leads to AB being parallel to CD. This is using the Converse of Corresponding Angles Theorem.
180 is the degrees a straight line segment is. This means that
4x + 3x + 2x = 180.
Since these all have the same variable (x), then you can add the coefficients. (4,3,2)
9x = 180
180/9 = x
X = 20
Oder of operations is this;